Vulkan: Don't defer clear for read render target We shouldn't collect deferred clears for the read render target because they get applied to the draw render target. This CL flushes stages updates to the read render target only if it's not the same as the draw render target. This can happen when the read render target is bound to another surface. Bug: b/192327017 Change-Id: I7c9e804f4eff10728aed7aeeaf41ef3869c9bdbd Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3125462 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Tim Van Patten <timvp@google.com>