We currently print reference type indices as unsigned LEB. This will not
work properly for large indices (>=64), as they will be interpreted as
negative indices when read back. They may also alias with builtin types.
In this CL, we fix this by defining builtin types as negative numbers.
We add positive byte constants that can be used in function bodies.
We adapt wasm-module-builder and tests to the above changes.

Bug: v8:7748
Change-Id: I4dfaa65d4cbf77a6731ca2283148bd842ea5c56b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3080569
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76176}