[graphite] Move contents of ImageUtils to TextureUtils.

Both contain helpers for SkImage and SkSurface related routines,
so consolidating.

Change-Id: Ie9ccde1401d8cb84ea741bff6315b304e53eb28b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/748302
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
10 files changed