TypeScript 3.8 `lib.d.ts` updates

[DanielRosenwasser]

• Ensure that PRs are merged in.
• Sync with https://github.com/Microsoft/TSJS-lib-generator/

[Kingwl]

It's a F# project last time I saw, doesn't it? 😅

[ExE-Boss]

Presumably, this includes #34065 and #33707.

[sandersn]

This is done now.