Add `matches` method to `ValType` and `FuncType`

[Robbepop]

Blocked by #774.

Wasmi currently has PartialEq and Eq derives on FuncType for comparisons.
After function-references Wasm proposal support has been added, those trait impls need to be removed as they do not support sub-typing. Instead, we need to add the following methods, as done in Wasmtime:

• ValType::matches
• FuncType::matches

cc @BoilingFusion