Update Blockly codebase to Typescript

Steps for this update. These are not necessarily in order, and some will be broken out as separate bugs.

• Add a tsconfig.json. (#5892)
• Wire the typescript compiler to output into the build directory such that the closure compiler picks up the correct files. (#5892)
• Add gulp tasks and scripts in package.json to run the ts compiler and then the closure compiler. (#5892)
• Add gulp tasks and scripts in package.json to clean up generated files when needed. (#5892)
• #5904
• #5960
• Convert jsdoc to typescript types + tsdoc (automated conversion).
• #5860
  • Create a list of files that could not be converted, with reasons.
• Set up API Extractor to roll up type definition files into a single file (#5854).

[daniel-brenot]

Part of this is that it may be prudent to separate some of the work for blockly into separate repositories for things such as generators for different languages.

[tolst0v]

coolconsole.log('cool')