Rename GrGLSLXferProcessor to GrXferProcessor::ProgramImpl

return from GrXP by unique_ptr, rename factory function to
makeProgramImpl()


Bug: skia:11358
Change-Id: Iff79b59c07229166d751b263c4cfcc84cb268e7a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437896
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
25 files changed