• [varLib] Use sentinel value 0xFFFF to mark a glyph advance in hmtx/vmtx as non participating, allowing sparse masters to contain glyphs for variation purposes other than {H,V}VAR (#3235).
• [varLib/cff] Treat empty glyphs in non-default masters as missing, thus not participating in CFF2 delta computation, similarly to how varLib already treats them for gvar (#3234).
• Added varLib.avarPlanner script to deduce 'correct' avar v1 axis mappings based on glyph average weights (#3223).