[khmer] Rewrite most of shaper to better follow spec
Khmer spec has only one reordering phase, and only simple prebase
matra and Coeng-Ro reordering. Implement that. Specifically,
this was done to address recognizing different orders of the matra
and Coeng-Ro sequence. That said, some combinations are now
reordered differently from Uniscribe. Not clear if that's intended
or a bug in Uniscribe. The following two sequences render the same
in Uniscribe whereas we reorder them differently:
U+17A0,U+17D2,U+179A,U+17C2
U+17A0,U+17C2,U+17D2,U+179A
For that reason, our test suite numbers regressed slightly. Used
to be at 34 for fails, now at:
KHMER: 299080 out of 299124 tests passed. 44 failed (0.0147096%)
But generally a good change, and removed lots of code.
Fixes https://github.com/harfbuzz/harfbuzz/issues/1026
3 files changed
