Add a chained struct for Dawn-specific options for SPIR-V ingestion to
contain this new flag.
Bug: tint:1890
Change-Id: I1332ff20c91f29a84c21550a37f11bc7d9c956ce
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/118421
Reviewed-by: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: James Price <jrprice@google.com>