Config option to separate or hide untracked files (addresses #35480)

[Jakobeha]

This PR adds an option to the Git extension, handleUntracked, which changes how it handles untracked files. The options are:

• withchanges: Untracked files are displayed with other changed files. My intention is that should not affect VSCode's current behavior
• separate: Untracked files are in a separate UNTRACKED section below the CHANGES section. When staging all changes, a dialog will ask the user if they want to include untracked files or not.
• hide: Untracked files are completely hidden from the changes list. They are also not counted in the badge (even if all is selected)

I figure this might need more work, or maybe it's not the best approach. But currently it makes it much easier to use VSCode's git capabilities for projects with a lot of untracked files.

Fixes #35480

[msftclas]

All CLA requirements met.

[joaomoreno]

Just some general comments. I like the overall approach. I'm going to give it a good test drive and a final review and will try to merge it today.

[joaomoreno]

These seem leftover changes.

[joaomoreno]

This misses a type.

[joaomoreno]

Did a lot of cleanup:

• Untracked decorations were missing.
• The Stage All command was behaving strangely. If there's a separate section, we should just have a separate Stage All Untracked action which does not ask about untracked files in the normal Stage All action.
• Same for the Discard All Changes command. The new Discard All Untracked Changes should only clean untracked files.
• We probably also want Stage All Tracked Changes and Discard All Tracked Changes commands.
• The smart commit action should also work differently based on the setting and just not include untracked changes, unless they are the only changes available.
• Renamed setting to untrackedChanges
• Renamed default option to default

[joaomoreno]

Great job overall, definitely the bulk of the work! Thanks! 🍻