When changing an InstrumentTrack's base note while NotePlayHandles are
active, they will send a wrong MidiNoteOff event due to the masterKey()
translation in InstrumentTrack::processOutEvent().
Therefore in NotePlayHandle remember the original base note value and
add the difference between original and current base note to the value
returned by NotePlayHandle::key(). Fixes hanging notes in MIDI-based
instruments such as ZynAddSubFX.
Furthermore some coding style improvements.
Closes#3146975.
a9717c0cc3