Implement voice stealing composite ADSR

[heuermh]

https://electronicmusic.fandom.com/wiki/Voice_stealing
https://forum.pdpatchrepo.info/topic/5311/polyphonic-voice-management-using-poly

[heuermh]

Also low-note, high-note, and last-note priority for monosynth ADSRs
https://electronicmusic.fandom.com/wiki/Note_priority

[heuermh]

VOICE STEALING The Digitone has eight voice polyphony. VOICE STEALING sets the rules for how voices are stolen (which voice is taken when you play a new note) when you use more than eight voices at the same time.

Press [LEFT]/[RIGHT] to select voice stealing mode.

CYCLE The first played note is stolen first.
TRACK Track priority. Notes played on track 1 has priority over notes played on track 2, 3, and 4. Track 2 notes over track 3, 4 Track 3 notes over track 4.
LOW Lowest note is stolen first
HIGH Highest note is stolen first.