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

Code like:

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

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

Fixes #61912: Account for the fact that modes can be instantiated before all extension points have been handled.

We compile using the alwaysStrict flag so these directives are not needed

This part removes most `use strict` directives that are right after the file header