FramebufferVk::updateRenderPassDesc() is resetting entire
mRenderPassDesc, which may lose color unresolve attachments. This CL
makes sure that when we toggle depth stencil buffer's read/write access,
we do not reset the whole mRenderPassDesc. Instead we only update the
depth stencil attachment's access.

Bug: b/168953278
Change-Id: Ia9df2d8ac81ebf2da8a360ba1293faf6c14b2738
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2426468
Commit-Queue: Charlie Lao <cclao@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>