In CommandBufferHelper::endRenderPass(), we are checking depth stencil's
initialLayout to change storeOp to None if the layout is read only. But
the layout was set after that check, which essentially voids the
optimization.  This CL moves the finalizeDepthStencilImageLayout() call
before the layout is used.

This CL also moves the depth stencil loadOp/storeOp to a new function
finalizeDepthStencilLoadStoreOp(). When depthImage gets deleted before
renderpass ends, we could also apply the same load/store optimization
just like we did at endRenderPass() time.

Bug: b/187425444
Change-Id: I89814274352f09cbf1f7b58a91bbaf131b983fb1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2877933Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Charlie Lao <cclao@google.com>