Based on experimenting with Uniscribe to extract grammar and categories.
Failures down from 44 to 35:
KHMER: 299089 out of 299124 tests passed. 35 failed (0.0117008%)
We still don't enforce the one-matra rule pre-decomposition, but enforce
an order and one-matra-per-position post-decomposition.
https://github.com/harfbuzz/harfbuzz/issues/667
I know it's bad form; I know I've said no to this multiple times...
But this is part of an experiment to see if we can make rolling HarfBuzz
into Chrome much faster. That will give us a lot more testing exposure
that currently Chrome does.
Doing this while those files are still considered ignored by our
gitignore rules; will see how that flies.