Improve widget specific status bar handling

[msujew]

What it does

Closes #14045

Adds a new dedicated WidgetStatusBarService (and associated WidgetStatusBarContribution) that enables showing status bar items for the currently selected widget.

If no WidgetStatusBarContribution matches the current widget (like if the Explorer was selected), the previous status bar items stay. If another widget like the notebook editor gains focus, the correct contribution is selected and the new status bar items are shown.

Some specific widgets (webview, custom editor, preferences, getting started, etc.) in vscode hide the previous status bar items. For this, we implement a noopWidgetStatusBarContribution function to enable easier disabling of status bar items.

How to test

1. Select a monaco editor widget.
2. Ensure that the expected status bar items appear
3. Select a different widget (like terminal, explorer)
4. Assert that the status bar items stay where they are
5. Select a notebook widget (and select a cell within)
6. Assert that the expected status bar items appear, and the editor ones disappear.
7. Select the getting started (or webview, custom editor, preferences, etc.) widget
8. Assert that all editor related status bar items disappear.

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

[jonah-iden]

Cool contribution!

Just having to add this noop to all special widget is not the nicest thing.
I still believe having some way to mark "main widget", meaning widgets that in vscode are normally always in the main area and thus affecting things like status bar items and active editor, etc. Then all these "main widgets" would automaticly just do the noop except if a contribution is registered for them.
This would then also greatly help with tracking the active text and notebook editor.
But thats probably something for later