Glyph reuse

Identify and exploit sets of shapes where for each set of shapes there exists one shape from which all the others in the set can be derived by application of a transform.

See existing code for this in nanoemoji:

- https://github.com/googlefonts/picosvg/blob/main/src/picosvg/svg_reuse.py, https://github.com/googlefonts/picosvg/blob/main/tests/svg_reuse_test.py
- https://github.com/googlefonts/nanoemoji/pull/414 - incomplete upgrade, the pattern here is good starting point for a fontmake-rs implementation

Implementation in fontmake-rs:

- Emit reuse information per-glyph after each glyph completes
- Once all glyphs complete merge them and figure out what is reusable