Handle complex types in assertion wrapper modules

[tlively]

Continuation types cannot be passed to JS, so assert_return actions must be implemented with WebAssembly wrapper modules when converting tests to JS. There is precedent for this with vector and exnref types. The difference for continuations is that they are defined types, so creating the wrapper modules with the correct import types requires arbitrarily complex type sections.

Add code to traverse and topologically sort the rec groups reachable from the type of an exported function or global, then map them back to surface syntax that can be emitted.

[rossberg]

Oh right, I hadn't realised that you need the type section, too!

I appreciate that you implemented all the machinery to minimise it. :) But is that complexity actually needed? Why not just copy the type section as is? For just driving a test, I don't think it matters whether the wrapper has redundant definitions in it, and the type sections in the test suite won't be huge.

[tlively]

Yes, I had the same thought. The problem is that the type section we have is in terms of recursive DefT, not type indices. Mapping the entire type section back to using type indices is no easier than just doing so for the types we need. (Or maybe there's a shortcut I didn't find?)

[rossberg]

I think the simplest solution would be to beef up the translation environment such that env.mods and env.insts record not just the exports but pairs them with the type definitions from the AST. Then of_wrapper could pass x_opt on to wrap, which could just look up the types there.