refactor(tests): Migrate generator tests to import shims; delete bootstrap.js (#7414)

* refactor(tests): Use shims instead of bootstrap to load Blockly

  - Modify tests/generators/index.html to import the test shims
    instead of using bootstrap.js to load Blockly.

  - Modify test/generators/webdriver.js to have it wait for the
    workspace to exist before calling loadSelected().  There was
    previously a race which index.html had been winning, but
    now webdriver.js is winning (and the tests failing because
    there is no workspace yet when start() is called.

* chore(tests): Delete bootstrap.js etc.

  - Delete bootstrap.js, bootstrap_helper.js, and bootstrap_done.mjs.
  - Remove remaining references to bootstrap.js

* refactor(build): Remove deps npm script

  buildDeps is now only needed by buildCompiled, not ever for
  runnning in uncompressed mode, so:

  - Remove the deps gulp task (and the deps npm script.
  - Have the minify task run buildJavaScript and buildDeps directly.

  Additionally, the buildAdvanceCompilationTest target hasn't
  needed deps.js for some time (if ever), so skip having it run
  buildDeps entirely.

* refactor(build): Repatriate DEPS_FILE to build_tasks.js

  Since this is no longer used anywhere else it doesn't need to
  live in common.js.

* fix(scripts): Remove vestigial references to deps.mocha.js

* docs(tests): Add additional explanatory note

scripts/migration/js2ts

@@ -54,7 +54,6 @@ goog.addDependency = function(relPath, provides, _requires, opt_loadFlags) {
 
 // Load deps files relative to this script's location.
 require(path.resolve(__dirname, '../../build/deps.js'));
-require(path.resolve(__dirname, '../../build/deps.mocha.js'));
 
 //////////////////////////////////////////////////////////////////////
 // Process files mentioned on the command line.