Express durations with or without tuplets according to context

[jacobtylerwalls]

music21 version
reproduced on current as well as 5.7.2

Problem summary
We have several use cases for automatic tuplet fixing. One of them is when a cross staff tuplet leaves a gap in one hand of piano music that has been separated. Using a quarter rest to fill the gap between two incomplete tuplets is a recipe for malformed musicxml output. The other use case for tuplet consolidation is if we end up creating more tuplets in #763. The humdrum parser calls duration.TupletFixer, but nobody else does. Maybe for v7, if we can swing it, we can look into getting this into the makeNotation/musicXML export pipeline. This might be a reason to put #763 on ice for now.

Steps to reproduce

s = stream.Stream()
s.append(note.Note(quarterLength=(1/6)))
s.insert((5/6), note.Note(quarterLength=(1/6)))
s.show()

Expected vs. actual behavior

Desired

Actual

More information
@napulen noticed in MarkGotham/When-in-Rome#17

[jacobtylerwalls]

Ah, right, you already mentioned this was the very long term goal to handle these streams in #763 (comment)

[napulen]

Just FYI, there may be other "real-world" pieces by Fanny Mendelssohn Hensel with very similar patterns, which also trigger this issue.

Thanks for the minimal example presented here.