Formalize rendering.Chord #284
Description
vexml currently mimicks the note data structure of vexflow: a Note can represent a single note or a chord. While it's convenient to overlap with vexflow, this causes problems downstream outside of rendering. For example, when calculating cursor state retrigger or sustain hints, we need to know which chord notes are connected by a curve.
I propose creating a rendering.Chord, which will be composed of many rendering.Note. After that, update playback.LazyCursorStateHintProvider to use this information to output hints more correctly.