getNoteGrowY

growY a note needs so its (centered) text fits; the note keeps its square width.

Returned in *unscaled* units — the label is measured at the scale the note is actually drawn at, and the overflow is then divided back out, because growY is stored as a number of unit-note pixels and multiplied by scale when the height is computed. Returning the scaled overflow instead is what made a note from a .tldr file, where the prop has always meant the unscaled thing, come out too short for its own text.