Make GrCaps and graphite::Caps derive from SkCapabilities

Move allocation of Caps::fShaderCaps to the base class,
and add a finishInitialization method, like GrCaps.

Change-Id: I5353a03afea29390be3cce1fb371374532f5af3c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/541073
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
22 files changed