Metal: only set stencil format in ProgramDesc if needed.

After adding framebuffer support in Metal, the validator is failing
because we're hitting cases where we're trying to use a pipelinestate
that assumes a stencil attachment to render to a framebuffer
without a stencil attachment. This CL addresses this issue.

Change-Id: I6e95f321aa5820a64a8084c457159f917c37a7c7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437119
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
1 file changed