Allows ANGLE to create Framebuffers and RenderPasses with a read-
only depth/stencil layout. Also allows us to transition our Images
to this new DepthStencilReadOnly layout.

Internal code redesign. No functional change to our command stream.

Bug: angleproject:4959
Change-Id: I9b80063bdaec8f5d6c89037e0618c85e1c11b78d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2354280Reviewed-by: Charlie Lao <cclao@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>