Allows you to infer the N'th parameter type of a function.
Change-Id: Iab7065cb37dbf1332cef601bca91894b8c6b4edf
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/35662
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>