Add cursorRedo command (Ctrl+Shift+J)

[SnirBroshi]

There is a command called cursorUndo which is used to undo cursor and selection changes.
The undo stack is flushed when the text changes.

This PR adds a cursorRedo command to complement cursorUndo, and binds it to Ctrl+Shift+J by default.

This fixes #82007

How to test

1. Open an empty buffer
2. Type some text
3. Move the cursor around with commands that do not modify the text itself. You can also select things and multi-select.
4. Press Ctrl+U a couple of times to undo some of those movements
5. Press Ctrl+Shift+J to redo each movement you just undid.
6. Modify the text - the undo/redo stack should be flushed and you should not be able to use cursorUndo/cursorRedo to get to the previous cursor locations.

Implementation

To do this I refactored the code to separate the part that interacts with the editor (CursorUndoController) from the cursor undo/redo logic (CursorStateStack).

Previously a list of cursor states was kept, and to undo the state it would pop the latest state from the list.

This PR changes that to a list of cursor states and an index to where we are currently inside that list.
When undoing or redoing the index is moved without deleting any states from the list.
When the state changes, all the states after where we are currently inside the list are dropped, and the new state is added.

[msftclas]

All CLA requirements met.

[SnirBroshi]

@alexandrudima you completely deleted my entire code without even leaving a comment. What gives?