Add Duplicate (Notes) Over action+shortcut in Piano Roll

[JJCUBER]

This implements the feature requested in #1876 which got put within a list in #1488 then moved to #4877 for improving UI/UX workflow.

Having a selection in the piano role then selecting this action or using Ctrl+D clones the notes in the selection and places them just past the end of the selection. Having no selection instead duplicates everything over (similar to how commands for moving notes move all of them when nothing is selected). The new notes become selected (and the old notes become unselected), allowing for quickly chaining Ctrl+D an arbitrary number of times.

In one of the aforementioned issues, there was discussion pertaining to potentially placing the notes at the end of all notes instead of just the selection as the default behavior. I am open to modifying the code to that if it is desired; however, I think the one I selected is a more sane default, as repeating what is selected should logically only care about itself, not the unrelated notes in the piano roll (e.g., if you have some arpeggio chord you want to repeat alongside your other notes and/or want to repeat then shift down). In fact, it would likely be better to potentially add three different actions (since the code for each changes only one line of logic):

1. place duplicates after selection (this pr)
2. place duplicates after all notes (alternate proposed in one of the issues)
3. place duplicates starting at next available bar/measure past the selection (a tertiary one I'm proposing)

Let me know what you think about the above and I can change anything as needed.

[regulus79]

Potentially related? #7873

[JJCUBER]

Ah yeah that does seem pretty similar, though some of the additions differ from the additions I proposed at the bottom of my pr. Annoyingly, that did not show up when I searched (not to mention, GitHub likes to search by individual tokens anywhere in an issue/pr, so search queries have to be overly specific and accurate to find anything).