Decouple SkSpecialImage from Ganesh and Graphite

This will help us build src/core without #defines

Bug: skia:14317
Change-Id: I39bfedd7e3712bd252bbca4c08d887f0d0b13980
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/723397
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
19 files changed