Migrate Graphite shader code into sksl_graphite_frag.

This allows us to pre-parse and analyze the code once at startup,
instead of every time a shader is assembled.

In order to make changes to `sksl_graphite_frag.sksl`, please set
`skia_compile_modules = true` in your GN args. This will cause the
dehydrated code to be regenerated at build time. This should not slow
down normal builds; it only rebuilds when dirty.

Change-Id: I08f2005399ea3a12726946db1e3f2c39f9c24df8
Bug: skia:13110
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/532398
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
3 files changed