refactor(generators): Migrate JavaScript generators to TypeScript (#7602)

* refactor(generators): Migrate javascript_generator.js to TypeScript

* refactor(generators): Simplify getAdjusted

  Slightly simplify the implementation of getAdjusted, in part to
  make it more readable.  Also improve its JSDoc comment.

* refactor(generators): Migrate generators/javascript/* to TypeScript

  First pass doing very mechanistic migration, not attempting to fix
  all the resulting type errors.

* fix(generators): Fix type errors in generator functions

  This consists almost entirely of adding casts, so the code output
  by tsc should be as similar as possible to the pre-migration .js
  source files.

* refactor(generators): Migrate generators/javascript.js to TypeScript

  The way the generator functions are added to
  javascriptGenerator.forBlock has been modified so that incorrect
  generator function signatures will cause tsc to generate a type
  error.

* chore(generator): Format

  One block protected with // prettier-ignore to preserve careful
  comment formatting.

  Where there are repeated concatenations prettier has made a pretty
  mess of things, but the correct fix is probably to use template
  literals instead (rather than just locally disabling prettier).
  This has been added to the to-do list in #7600.

* fix(generators): Fixes for PR #7602

* fix(generators): Fix syntax error

generators/javascript/variables_dynamic.ts

@@ -0,0 +1,17 @@
+/**
+ * @license
+ * Copyright 2018 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @fileoverview Generating JavaScript for dynamic variable blocks.
+ */
+
+// Former goog.module ID: Blockly.JavaScript.variablesDynamic
+
+// JavaScript is dynamically typed.
+export {
+  variables_get as variables_get_dynamic,
+  variables_set as variables_set_dynamic,
+} from './variables.js';