* adopt in tests

* adopt more join() that are straight forward

* more safe usages

* more adoption

part of strict null work

Throw not implemented instead of returning null results for most methods

More manual conversion of index based for loops to for-of loops

Replaces many loops of the form:

```js
for (let i = 0; i < elements.length; ++i) {
    const i = elements[i];
   ...
}
```

with:

```js
for (const element of elements) {
    ...
}
```

Mix of a horrible regex based find/replace and manual touch ups

This reverts commit 5897b877.

Continues #60565 for converting tests. A few files used TypeStat to add `!`s but the following interface changes were manually inferred from implementing classes:
* `IActiveCodeEditor`'s methods can all return `null`
* `IEditor` needs to report `getControl(): IEdotorControl | null` because `BaseEditor`'s `getControl` can return `null`

* 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`

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)[]`