Now that all backends use slab-allocated bind groups, this patch also
moves the BindGroup implementation with owned-data into the Null backend.
Bug: dawn:340
Change-Id: I08a952075b382008fb82f1fbab3f779cc05bc2a3
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/16747
Commit-Queue: Austin Eng <enga@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>