Moving pianoroll changes into new PR.

[blackears]

Resolves: (direct link to the issue)

(short description of the changes and the motivation to make the changes)

• [ ] I signed CLA
• [ ] I made sure the code in the PR follows the coding rules
• [ ] I made sure the code compiles on my machine
• [ ] I made sure there are no unnecessary changes in the code
• [ ] I made sure the title of the PR reflects the core meaning of the issue you are solving
• [ ] I made sure the commit message(s) contain a description and answer the question "Why do those changes fix that particular issue?" or "Why are those changes really necessary as improvements?"
• [ ] I made sure the commit message title starts with "fix #424242:" if there is a related issue
• [ ] I created the test (mtest, vtest, script test) to verify the changes I made

[blackears]

This replaces https://github.com/musescore/MuseScore/pull/9033 which has gotten unmanageable.

[RobFog]

A rebase is needed.

[blackears]

Looks like Github just upgraded its security. I need to change all my keys first.

[Jojo-Schmitz]

One unit test failed, see https://github.com/musescore/MuseScore/runs/5579586289?check_suite_focus=true#step:8:1231

I believe the reason is https://github.com/musescore/MuseScore/pull/9109#discussion_r828859482

[scorster]

Just adding a link to Piano Roll Editor bug reports and requests located in the MuseScore discussion area.

https://github.com/orgs/musescore/discussions/16925