A piano roll lock ghost nodes button.

### Enhancement Summary
Basically an "inking" mode in the piano roll.
I'm mainly a drawing artist, so this idea naturally comes from inking step when doing 2D artwork on a drawing application.
The idea would be to lock everything that isn't under the ghost notes like when you lock the alpha button of a 2D layer on photoshop/Krita.
Basically the only valid input when recording with a keyboard or drawing with a mouse will be the areas inside the ghost notes.

#### Justification
This could help stuff like recording much easier, like you lay out with the mouse some chords or a melodic line, then simply record again on top using a MIDI keyboard and automate that way "inking" the mouse notes with your keyboard, and overriding things like dynamics.
Also, the recording when inking could only progress when notes are only being held, making it even easier to "ink" in a slowly way things like dynamics and notes micro off sync or not being of a perfect lenght, which are like huge deals when recording using a MIDI keyboard.

#### Mockup
A button next to the ghost notes icon, or could be a toggled alpha icon/background on top of the ghost notes button.

Start by locating the piano roll implementation and the existing ghost-notes control. Clarify the proposed input-locking and recording behavior before choosing an implementation path. Done would mean a defined, usable lock mode that restricts mouse and MIDI input to ghost-note areas and has appropriate verification.

Written by the indexing model from the issue text.