Refactor undo-redo action for editors

[msujew]

What it does

Closes #13962
Closes #9344

Refactors our undo/redo mechanism to better support different kinds of editors. Adds a UndoRedoHandlerService that keeps a list of UndoRedoHandler contributions. This design is heavily influenced by how VS Code handles its undo/redo across different editors. See also microsoft/vscode#98288.

How to test

Follow the reproduction steps from #13962 and #9344 and assert that the undo/redo action is only ever executed on the currently selected editor. Also:

• Assert that undo/redo on normal text inputs (like the extension search bar) still works as expected even in the presence of a text editor in the main area.
• Assert that the undo/redo falls back to the last active monaco editor in case no widget is selected that is capable of performing an undo/redo action.

Follow-ups

Using this architecture, we could add support to undo/redo actions in the navigator. VS Code for example allows to undo file deletion/rename/move. We can do that in a separate PR though.

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

[jbicker]

Works as expected now. Thanks!