Converting features from .ufo to .glyphs should allow invalid code

[schriftgestalt]

I’m trying to roundtrip a .glyphs file that happens to have outdated classes with some glyphs that are not in the font.

in def _to_glyphs_features() (in features.py), > FeaDocument() > self._doc = parser_.parse() > featureLib.parser.Parser.parse() it checks for missing glyphs. But all we want is to segment the .fea file into individual feature blocks. The code should not required to be valid.

[khaledhosny]

Possibly related to fonttools/fonttools#3501.