* 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.

ES6 promises like using undefined as their first argument instead of null. Both should behave the same behavior

Overwrite implies that the setting will be changed rather than superseded.

In these cases, the programmer has explicitly indicated that the type should be nullable