Move atlas -> shader conversion up to SkCanvas

This makes the SkDevice interface and code simpler, and also opens the
door to a version of drawAtlas that takes a more complex SkShader (on
the SkPaint), rather than just a single SkImage.

Bug: skia:11942
Change-Id: I557bd2f03b85940b29954cb994916d5566bd7747
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/458980
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
14 files changed