Implement the Wasm branch-hinting proposal

[Robbepop]

This is about adding support for the branch-hinting Wasm proposal.

The branch-hinting Wasm proposal has been recently moved to Phase 4 and thus stabilization can be expected to happen soon.

Since branch hints won't be that effective in Wasmi we probably only want a facade support for them so that Wasm modules using them are simply validating properly but otherwise the branching hinting information is ignored.