[spirv-reader] Check for invalid types early in parser

We are currently relying on validation during later transforms to
detect these unsupported types. This does not play well with an
upcoming CL that makes these validation steps assertions. It also
means that we sometimes accept these types if they are not actually
used.

Change-Id: Ibea0716e2d91ae7f193b47130b8eb3eebd9f9f02
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/299895
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>