Tech debt: `NotationNoteInput::state()` can probably be optimised

[cbjeukendrup]

This method seems to be called very often; while simply updating the state of the note input bar once, it is already called maybe 10 times. While this method is not very expensive, it is not completely trivial either, and it is very redundant to call it again and again.

We could either cache the mu::notation::NoteInputState, or just eliminate it completely and use mu::engraving::InputState directly.

(This just caught my attention while debugging something else; perhaps it is not significant enough to spend time on. Feel free to close in that case.)

Not sure if exactly related, but something I noticed lately (in a large score, so there's a bit of lag generally): in note input mode, I'd sometimes click to change duration, or add a dot, and the toolbar UI would seem to change immediately, but if I was too quick at typing a letter name, a note of the previous duration would actually be input. I could avoid this by waiting a second, but it was very disconcerting.

[bkunda]

If this is likely to result in any discernible performance improvement, I'd be keen to see this bumped up in its order of priority.