We are tracking depth and stencil read or write during the renderpass.
We can use that to switch to DepthStencilReadOnly layout if both depth
and stencil are not writing. This allows drivers to optimize out the
storeOp for the renderpass.

Bug: b/168953278
Change-Id: Id82e06b4bae1ae8c83d880bb5e58accfa61f8191
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2411336
Commit-Queue: Charlie Lao <cclao@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>