Stretch/Shrink/Shorten Patterns via SongEditor

For some time we've had the ability to stretch a piano roll pattern in the piano roll editor via `Select All` and the `Shift` modifier key when dragging a note.


Possible functionality:
1. Open Song Editor
2. Create a new Piano Roll pattern
3. Draw some notes
4. Go back to Song Editor
5. Hold shift and resize Piano Roll pattern
6. Piano roll pattern shrinks in size and notes shrink to scale with pattern.

**Similar to this current functionality:** (animation courtesy of Uros).

This is an enhancement request to add the same functionality to the Song Editor window, including shortening capabilities. :)

Start by locating the Song Editor's Piano Roll pattern resizing behavior and the existing piano roll stretch implementation. Reproduce the described workflow, then verify that shift-resizing a pattern in Song Editor shortens or stretches its notes proportionally.

Written by the indexing model from the issue text.