refactor(build): Preparation for building TypeScript (#6205)

* chore(deps): Update closure/goog/base.js, add goog.js

  - Update base.js from the latest version (20220502.0.0).
  - Also copy over goog.js, which provides access to a suitable subset
    of goog.* via an importable module).

* chore(build): Split gulpfiles/config.js exports object

  This makes it possible for entries to depend on each other.

* chore(build): build config consistency

  - Reorder entries in gulpfiles.config.js to better match order they
    are used.
  - Have update_metadata.sh reference config.js and vice versa.

* refactor(build): Move deps.js (+ deps.mocha.js) from test/ to build/

  Once we start using tsc, deps.js will be created based on the ouptut
  of tsc rather than the raw source in core/.  Since tsc will need to
  be run before running closure-make-deps and also before trying to
  load blockly_uncompressed.js, it doesn't really make sense to check
  in deps.js; it's better to re-create as needed.

  To reduce inconvenience, a new "prepare" script is added to
  package.json which will run the buildDeps gulp target automaticaly
  when one runs npm install.

* refactor(build): Always build from TypeScript sources

  - Add buildJavaScript gulp task to use tsc to compile any .ts files
    in core/ into build/src/core/ (and also copy any .js files that
    are not yet migrated to TypeScript, which for now is all of them.
  - Remove closure/goog from explicit inputs to tsc; it will find
    the files it needs (e.g., goog.js) automatically.
  - Have buildDeps, the playground, and all the tests that run in
    uncompiled mode use build/src/core/ instead of core/ as their
    input directory.

* feat(build): Add buildJavaScriptAndDeps gulp task

  Have npm run build:deps (and npm run prepare) use a new gulp task,
  buildJavaScriptAndDeps, to run tsc followed by closure-make-deps,
  ensuring that deps.js is calculated based on the most recent code
  in core/.

* fix(build): Fix implementation of flattenCorePaths

  Even though this function is going away I want to remove it in
  a separate PR so that we can revert easily if desired.  But the
  previous checked-in code was totally wrong.  This version works.

* fix(build): Don't let checkinBuilt copy build/src/**

  Now that we are putting a lot more stuff in build/ (specifically,
  all the tsc output in build/src/), modify checkinBuilt so that it
  only copies the specific things we want to check in (for now):

  - _compressed.js build artifacts and their accompanying .js.maps
  - the generated build/msg/js/*.js language files.

  Unrelatedly, also fix safety-quoting of arguments for one execSync
  call.

closure/goog/base.js

@@ -256,15 +256,15 @@ goog.LOCALE = goog.define('goog.LOCALE', 'en');  // default to en
 
 
 /**
- * This method is intended to be used for bookkeeping purposes.  We would
- * like to distinguish uses of goog.LOCALE used for code stripping purposes
- * and uses of goog.LOCALE for other uses (such as URL parameters).
+ * Same as `goog.LOCALE`, which should be used instead.
  *
- * This allows us to ban direct uses of goog.LOCALE and to ensure that all
- * code has been transformed to our new localization build scheme.
+ * Using this method just makes it harder for closure-compiler to optimize
+ * your locale-specific code, since it has to take the extra step of inlining
+ * this function to discover and remove code that is not used for the target
+ * locale.
  *
  * @return {string}
- *
+ * @deprecated use `goog.LOCALE`
  */
 goog.getLocale = function() {
   return goog.LOCALE;
@@ -917,14 +917,6 @@ goog.global.CLOSURE_NO_DEPS;
 goog.global.CLOSURE_IMPORT_SCRIPT;
 
 
-/**
- * Null function used for default values of callbacks, etc.
- * @return {void} Nothing.
- * @deprecated use '()=>{}' or 'function(){}' instead.
- */
-goog.nullFunction = function() {};
-
-
 /**
  * When defining a class Foo with an abstract method bar(), you can do:
  * Foo.prototype.bar = goog.abstractMethod
@@ -1567,34 +1559,6 @@ goog.partial = function(fn, var_args) {
 };
 
 
-/**
- * Copies all the members of a source object to a target object. This method
- * does not work on all browsers for all objects that contain keys such as
- * toString or hasOwnProperty. Use goog.object.extend for this purpose.
- *
- * NOTE: Some have advocated for the use of goog.mixin to setup classes
- * with multiple inheritence (traits, mixins, etc).  However, as it simply
- * uses "for in", this is not compatible with ES6 classes whose methods are
- * non-enumerable.  Changing this, would break cases where non-enumerable
- * properties are not expected.
- *
- * @param {Object} target Target.
- * @param {Object} source Source.
- * @deprecated Prefer Object.assign
- */
-goog.mixin = function(target, source) {
-  for (var x in source) {
-    target[x] = source[x];
-  }
-
-  // For IE7 or lower, the for-in-loop does not contain any properties that are
-  // not enumerable on the prototype object (for example, isPrototypeOf from
-  // Object.prototype) but also it will not include 'replace' on objects that
-  // extend String and change 'replace' (not that it is common for anyone to
-  // extend anything except Object).
-};
-
-
 /**
  * @return {number} An integer value representing the number of milliseconds
  *     between midnight, January 1, 1970 and the current time.
@@ -1773,6 +1737,71 @@ if (!COMPILED && goog.global.CLOSURE_CSS_NAME_MAPPING) {
   goog.cssNameMapping_ = goog.global.CLOSURE_CSS_NAME_MAPPING;
 }
 
+/**
+ * Options bag type for `goog.getMsg()` third argument.
+ *
+ * It is important to note that these options need to be known at compile time,
+ * so they must always be provided to `goog.getMsg()` as an actual object
+ * literal in the function call. Otherwise, closure-compiler will report an
+ * error.
+ * @record
+ */
+goog.GetMsgOptions = function() {};
+
+/**
+ * If `true`, escape '<' in the message string to '&lt;'.
+ *
+ * Used by Closure Templates where the generated code size and performance is
+ * critical which is why {@link goog.html.SafeHtmlFormatter} is not used.
+ * The value must be literal `true` or `false`.
+ * @type {boolean|undefined}
+ */
+goog.GetMsgOptions.prototype.html;
+
+/**
+ * If `true`, unescape common html entities: &gt;, &lt;, &apos;, &quot; and
+ * &amp;.
+ *
+ * Used for messages not in HTML context, such as with the `textContent`
+ * property.
+ * The value must be literal `true` or `false`.
+ * @type {boolean|undefined}
+ */
+goog.GetMsgOptions.prototype.unescapeHtmlEntities;
+
+/**
+ * Associates placeholder names with strings showing how their values are
+ * obtained.
+ *
+ * This field is intended for use in automatically generated JS code.
+ * Human-written code should use meaningful placeholder names instead.
+ *
+ * closure-compiler uses this as the contents of the `<ph>` tag in the
+ * XMB file it generates or defaults to `-` for historical reasons.
+ *
+ * Must be an object literal.
+ * Ignored at runtime.
+ * Keys are placeholder names.
+ * Values are string literals indicating how the value is obtained.
+ * Typically this is a snippet of source code.
+ * @type {!Object<string, string>|undefined}
+ */
+goog.GetMsgOptions.prototype.original_code;
+
+/**
+ * Associates placeholder names with example values.
+ *
+ * closure-compiler uses this as the contents of the `<ex>` tag in the
+ * XMB file it generates or defaults to `-` for historical reasons.
+ *
+ * Must be an object literal.
+ * Ignored at runtime.
+ * Keys are placeholder names.
+ * Values are string literals containing example placeholder values.
+ * (e.g. "George McFly" for a name placeholder)
+ * @type {!Object<string, string>|undefined}
+ */
+goog.GetMsgOptions.prototype.example;
 
 /**
  * Gets a localized message.
@@ -1791,16 +1820,8 @@ if (!COMPILED && goog.global.CLOSURE_CSS_NAME_MAPPING) {
  * produce SafeHtml.
  *
  * @param {string} str Translatable string, places holders in the form {$foo}.
- * @param {Object<string, string>=} opt_values Maps place holder name to value.
- * @param {{html: (boolean|undefined),
- *         unescapeHtmlEntities: (boolean|undefined)}=} opt_options Options:
- *     html: Escape '<' in str to '&lt;'. Used by Closure Templates where the
- *     generated code size and performance is critical which is why {@link
- *     goog.html.SafeHtmlFormatter} is not used. The value must be literal true
- *     or false.
- *     unescapeHtmlEntities: Unescape common html entities: &gt;, &lt;, &apos;,
- *     &quot; and &amp;. Used for messages not in HTML context, such as with
- *     `textContent` property.
+ * @param {!Object<string, string>=} opt_values Maps place holder name to value.
+ * @param {!goog.GetMsgOptions=} opt_options see `goog.GetMsgOptions`
  * @return {string} message with placeholders filled.
  */
 goog.getMsg = function(str, opt_values, opt_options) {
@@ -2266,8 +2287,8 @@ if (!COMPILED && goog.DEPENDENCIES_ENABLED) {
       var src = script.src;
       var qmark = src.lastIndexOf('?');
       var l = qmark == -1 ? src.length : qmark;
-      if (src.substr(l - 7, 7) == 'base.js') {
-        goog.basePath = src.substr(0, l - 7);
+      if (src.slice(l - 7, l) == 'base.js') {
+        goog.basePath = src.slice(0, l - 7);
         return;
       }
     }

closure/goog/goog.js

@@ -56,7 +56,6 @@ export const isObject = goog.isObject;
 export const getUid = goog.getUid;
 export const hasUid = goog.hasUid;
 export const removeUid = goog.removeUid;
-export const mixin = goog.mixin;
 export const now = Date.now;
 export const globalEval = goog.globalEval;
 export const getCssName = goog.getCssName;
@@ -65,7 +64,6 @@ export const getMsg = goog.getMsg;
 export const getMsgWithFallback = goog.getMsgWithFallback;
 export const exportSymbol = goog.exportSymbol;
 export const exportProperty = goog.exportProperty;
-export const nullFunction = goog.nullFunction;
 export const abstractMethod = goog.abstractMethod;
 export const cloneObject = goog.cloneObject;
 export const bind = goog.bind;