In favor of separate VARC table.
ttGlyphSet does NOT yet know how to draw VARC table though.
The 9 failing tests are all VarComposite-related and need
to be updated with VARC equivalents eventually when we
add VARC support to subsetter and instancer.
Speeds up compiling of fonts with lots of composite glyphs.
For example, 40% speedup in decompile/compiling Handjet font:
./fonttools ttLib Handjet\[ELGR,ELSH,wght\].ttf -t'*' -o out.ttf
