* Converted another ~70 test files to strictNullChecks

These are the remaining test files that didn't require any changes to non-test file types. I'll send those in separately.

Most changes were automatic and small (`!`s).
The only non-trival change is that `extHostSearch.ts` needs an interface for its test data.

Again used [TypeStat](https://github.com/JoshuaKGoldberg/TypeStat) when possible per #65581. I'm happy to split this up into smaller PRs if you'd prefer!

* Added missing `!`s to `commands.test.ts`

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

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

* remove more TPromise (for #53526)

* fix failing webview integration tests on macOS

* do not instantiate TPromise (fix #62716)

* more TPromise removal and fixes

* 💄

* 💄

without instead of wihtout

Overwrite implies that the setting will be changed rather than superseded.

fixing simple cases of any[]

Add typings for the pattern: `let x = []` which defaults to `let x: any[] = []`

#60565

This code pattern indicates that the type should be nullable

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

* Added a new enum for setting types
* Added separate `Delayer` with a long debounce for non-text inputs