Remove SkSpecialImage::makeTextureImage

Tweak how SkImageSource works, so that all nodes now remain on the GPU,
or go directly there if we've got a GPU-backed skif::Context.

Bug: skia:9825
Bug: skia:10202
Change-Id: I35471fd41a00a0a9859eff04c26382e9d2d88a7b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/298347
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
6 files changed