[graphite] Move id off of UniformData and into UniformCache

Also renames UniformCache::findOrCreate() to insert(), and has it return
the assigned id. ExtractCombo() now does not take a UniformCache, since
it just has to return the CPU data extracted from the PaintParams. The
caching/id assignment is the responsibility of the DrawPass.

Updates unit tests and DrawPass to use this instead.

Bug: skia:12466
Change-Id: Ib363fcad799f62d0ad31bb9d3e4c995e191cae80
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/475798
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
7 files changed