Guarantee that QuickPickService.showQuickPick resolves on hide

[colin-grant-work]

What it does

Fixes #11067 by ensuring that the promise returned by QuickPickService.showQuickPick will be resolved by modifying MonacoQuickInputService to resolve undefined after the quick pick is hidden. If the promise has already been resolved, the second resolution will have no effect, and if it hasn't, it will be resolved with undefined.

How to test

1. There is an included test commit (with a lint error as a reminder to remove it). Run the command Test QuickPickService.show.
2. If you make a selection, you should see a log reflecting that selection.
3. If you close the quick pick without making a selection (e.g. hitting Esc or unfocusing the quick pick by clicking elsewhere), you should see a log reflecting a selection of undefined.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[vince-fugnitto]

I confirmed the changes work as expected, and resolve the issue 👍

[colin-grant-work]

Since this PR does not change dependencies, I deem that it is not the cause of the 3pp failure.