Defer stencil attachment until opsTask execution

Change-Id: I34cc35d16966d35e26561c40a0300112b2da2fa1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/253546
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
10 files changed