The latter is more explicit, correctly handles some edge cases, and helps tag places in the code where we should look into replacing null with undefined.

Enables strict null checking for `textEditorModel`. I also had to add a few null supressions to difficult errors.

* adopt in tests

* adopt more join() that are straight forward

* more safe usages

* more adoption

part of strict null work

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

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

* remove more TPromise (for #53526)

* fix failing webview integration tests on macOS

* do not instantiate TPromise (fix #62716)

* more TPromise removal and fixes

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