Part of #63832

Fixes #64812

* Manually added strict null checks in around 70 files

* Fixed tsconfig.strictNullChecks.json merge fail

* Touched up a few unnecessary type changes

* Removed files already in other PRs

We can revert this before stable if there are bit issues, but the fact that
#57803 goes away is pretty big.

Code like:

```
private readonly _onDidEncounterLanguage: Emitter<LanguageId> = new Emitter<LanguageId>();
```

Does not need to repeat the `Emitter<LanguageId>` type annotation

- Remove AUTHORS file
- Support lineHeight in demo
- Remove jsdoc dependency
- Layering refactors
- Buffer optimizations
- Whitespace/null cell differentiation
- Parser OSC string optimization
- Add missing break to setOption code
- Fix mouse coords when position: fixed is used
- Fix addon typings error
- Dispose atlas when no terminals use it
- Find as you type/incremental searching (+ line cache)

Fixes #65318

- False now really means false
- The default is true for all platforms

Fixes #65037

Fixes #65035

Part of #65035

Part of #65035

Part of #64390

Fixes #64865

Part of #60565

Coalesce has the correct return type of `T[]`. Filter may return `(T | undefined)[]`

Fixes #63688

These typing errors were hidden by us previously using `any`

Fixes #63223

* remove more TPromise (for #53526)

* fix failing webview integration tests on macOS

* do not instantiate TPromise (fix #62716)

* more TPromise removal and fixes

* 💄

* 💄

Fixes #25310