[graphite] Use approximate-sized scratch textures

Bug: b/311178538
Change-Id: I974a62cdbd2932186b2a531aaf73df76a64f8a1f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/781996
Commit-Queue: James Godfrey-Kittle <jamesgk@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
20 files changed