Nested smart components don't get variated

Noto Sans Math had `_part.braceright` (a smart glyph) which was itself implemented as a horizontally flipped component of `_part.braceleft` (another smart glyph). The nested component was not being variated, but copied directly into users of `_part.braceright`. I had to ensure that all glyphs starting with `_part.` had their components decomposed before it would work.

Reproduce the issue with the Noto Sans Math example and inspect how glyphs beginning with `_part.` and nested smart-glyph components are handled. Trace the component decomposition and variation path; done means nested smart components are decomposed and correctly variated instead of copied directly into their users.

Written by the indexing model from the issue text.