PartialInstancer-VF.ttx: add composite glyph and vhea table
PartialInstancer-VF.ttx: add composite glyph and vhea table

the glyph 'minus' references 'hyphen' as component, but doesn't have any deltas in gvar.

vhea table is required when vmtx is present.

fonttools/fonttools,googlefonts/fonttools