Remap all resources into a flat namespace, to allow tests to pass when
multiple resources use the same binding number.
Fixed: tint:959
Change-Id: I58ed07c789e1ea90fc370ceba73b9d8292902549
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/61261
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>