[clang] [llvm] [WebAssembly] Add support for nonnull_extern_ref type (PR #148935)

[Paulo Matos via llvm-commits]

https://github.com/pmatos requested changes to this pull request.

I have added a few ideas that we can improve the PR with but then we we'll still need some further passes to improve on the types behaviour.

https://github.com/llvm/llvm-project/pull/148935