Always attach stencil buffers with exact sample count matches

After this CL we will always attach a stencil buffer for rendering
that matches the stencil sample count of the proxy. We will even
downgrade a stencil attachment to one with less samples if necessary.
(In the past we would only guarantee that the attached stencil buffer
had a sample count >= to that of the proxy.)

Change-Id: I358e13ffdf286695257b1b5b672a84d16c417b80
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/253547
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
3 files changed