For #70020

* ext: in setting editor

- Scope machine settings
- Make remote settings scoped to machine settings

Code like:

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

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

Many `Promise.resolve(null)` should actually be `Promise.resolve(void 0)`. In other cases, we were missing a null return annotation.