Requires polyfilling for all but the MSL backend.
CTS tests: https://github.com/gpuweb/cts/pull/1002
Bug: tint:1367
Change-Id: I0cf56b74c01f30436f9ad00595a554a4042587e4
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/81501
Reviewed-by: David Neto <dneto@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Ben Clayton <bclayton@google.com>