Move builtin_to_string() and builtin_type() to
the CanonicalizeEntryPointIO transform. Use the former to
rename entry point IO variables to the gl_ names, and the latter
to cast values to the correct type.
Change-Id: Iddfad574ddd660ff1bfd89a399a001b967b6b67e
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/78380
Reviewed-by: James Price <jrprice@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>
0b39270e01