Also renames the h and cpp files to ResourceVk (to keep distinct from
other resource.h/cpp files) and renames 'onResourceAccess' to 'retain'.
Cleans up a few remaining mentions of the command graph in comments.

Bug: angleproject:4029
Change-Id: Ifc8e880c8cea3fc48a4aec4730191c88aa35a076
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2065920
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>