This generalizes the read tracking into read/write. Knowing the write
access can let us determine if we can switch a RenderPass to a read-
only mode. And switching to read-only will let us combine some
RenderPasses in Manhattan.

Bug: angleproject:4959
Change-Id: Ic97547e84fef4a2670437677000d4525006ef69f
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2358771
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Ian Elliott <ianelliott@google.com>