Use GrResourceProvider::MakeApprox for mask filter proxy sizes

This allows us to demand exact matches in size and eliminate our
dependence on absClear.

In the future we can take this a step further and offset the mask to
leave a transparent border on all sides, thereby creating a "decal"
effect.

Bug: skia:
Change-Id: I8cd02ba1365ace0ccaae250a7195f51d0c77ce8d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/242720
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
4 files changed