JS->TS: Port project from JavaScript to TypeScript

[britalmeida]

The renderer and watchtower were initially developed in JS, but this led to constant problems and time wasted in debugging mistakes with poor error reporting.
TypeScript should help with typing safer code and having better tools and static code analysis instead of things going 'undefined' sometimes :) Although it's work to convert the full project, it should be a worthy investment considering the amount of sadness that went into trivial mistakes.

• Add TS to the pipeline.
• Add type hints to the code progressively.
• Fix errors found by the static analysis.
  • Address spurious?? issue that array of strings is reported as string|null because of array iteration (shading.js)
  • ExampleManyImages: error passing in uiConfig object
• All code in TS
  • Is Index.js still needed?
• Enable the most pedantic set of errors, no 'any', strict null checks etc.
• Imports are working correctly (example problem in ExampleManyImages?)
• All IDEs and settings enabled. No errors left :)
  • Sometimes warnings spam when running yarn install. (ESBuild?)

[britalmeida]

Option that caused

spurious?? issue that array of strings is reported as string|null because of array iteration (shading.js)

is disabled pending a reply in microsoft/TypeScript#55206

[britalmeida]

Sometimes warnings spam when running yarn install. (ESBuild?)

Seemingly an ESBuild problem which would get solved by upgrading to yarn 3:
evanw/esbuild#789