Create keybindable action for "break multibar rest"

Big band parts: there's going to be both moments where we need multibar rests (arranged moments where an instrument must be quiet), and moments where we need the instrumentalist to have access to the chord structure while having no specific note on the staff (solos improvising on chord structure).
As a result, any time a chord lasts two measure, we have to break the multibar rest - or copypaste the previous chord then turn it invisible. The latter is currently easier than going through the menu for each measure, but creates needless clutter of items in the program. Having a shortcut (even not assigned by default) for the former would be preferrable.