Implement `Hash` on types

[RReverser]

Currently even data enums and structs (e.g. Type, FuncType, NameEntry, etc.), are missing Hash implementation, which makes it hard to use them in a HashMap for caching.

Would it be possible to add simple #[derive(Hash)] to all non-builder structs?

[RReverser]

@fitzgen I suspect you tagged / closed the wrong issue with that commit.

[fitzgen]

ah this was accidental, as part of merging wasm-smith into this repo. woops!