Vulkan: Optimize color clears vs read-only depth/stencil switch When switching to read-only depth/stencil mode, if the aspect that intends to be in read-only mode has a deferred clear, the clear is flushed separately beforehands (as that would be a write operation). Prior to this change, _all_ deferred clears were flushed for simplicity. In this change, only the aspect that is switching modes is cleared, leaving the other aspects free to be optimized as loadOp of the following render pass. Bug: angleproject:378058737 Change-Id: Iba4371590bee99f5022575c09b0d32231562488c Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6019829 Reviewed-by: Amirali Abdolrashidi <abdolrashidi@google.com> Reviewed-by: Charlie Lao <cclao@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>