Split notes more intelligently when placing a shorter note over a longer one

Currently:

https://github.com/user-attachments/assets/245a5ac1-dfd7-43d5-82ec-297fc80e77e2

See this comment for some explanation of what's going on.

Rather than this unexpected repeated subdivision, the duration of the newly-added short note should be subtracted from the longer one, which then should be notated in the simplest sensible way, something like:

(The contrived third measure is arguable; the above image is the result of me adding ties and then using the 'Regroup rhythms' tool, which logic could be leveraged here. That logic itself is in need of improvement, as requested elsewhere, so any such improvements would also benefit this behaviour.)

OR it could create a chord - see Zac's comment below (or perhaps do either, depending on a keyboard modifier - whatever it does it shouldn't do what it does now)