Allow copy and paste text

I would note this works for lots of other things - chord symbols, lyrics, articulations, etc. But each needs to be handled individually, because we actually do thing differently in terms of how to handle cases where the source and destination have different rhythms. Eg, if the source has four quarter notes and the destination has four half notes, do we copy things note-to-note or beat-to-beat - and if we copy beat-to-beat, how to we handle beats with no notes currently? If you compare how this works with chord symbols versus dynamics versus lyrics, you'll see three different approaches, each crafted to fit what seemed to make the most sense based on the meaning of those symbols. For staff text, there is no inherent meaning, so it's harder to know what makes the most sense. So some actual real world examples of where one would plan to use this, so we can discuss what the proper behavior should be.

FWIW, my gut feel is we should probably handle staff text like dynamics, where we copy according to beat position, but skip beats that don't have a note there.