Go wasi code converge

[tsahee]

Two comments on that:

• currently there is a little code duplication between jit and arbitrator - in that both need to call wrap! macros for every arbcompress / wasip1 function. There is no logic in that duplication, though.
• End goal is to have Uptr be a separate type that's still u32 in wasm, but in rust does not have automatic casting casting to/from u32, and have read/write functions only accept that type.

[rachel-bousfield]

Looks great! Nice work :D