Allow the resolver to understand builtin structures, like
__frexp_result_f16. This allows backend transforms to declare the types,
even if they're "untypable" by the user.
Bug: chromium:1430309
Change-Id: I392709118182a058f737ccf1b7b46fc6b0b7264d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/129482
Kokoro: Ben Clayton <bclayton@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
47dd30117d