When a track is deleted, the bottom-most track should become selected

https://github.com/audacity/audacity/issues/11179 fixes the track focus state after deleting the bottom-most track in the project.

This ticket is intended to improve the UX when deleting tracks by addressing the following two issues:

1. After deleting the bottom-most track and undoing the action (Ctrl+Z), the focus doesn't move to the track that is now at the bottom, even though it should.
2. Once a track in the project is deleted, the next track should not only be in focus (current behavior) but also selected so that pressing Delete/Backspace would delete that track immediately. At the moment, you have to select the track manually each time.

No source files or tests are named. Start by reproducing deletion of the bottom-most track, undo it with Ctrl+Z, and then delete a track in a multi-track project; done means focus moves to the new bottom track after undo and the next track is also selected for immediate deletion.

Written by the indexing model from the issue text.