components: Text format does not disambiguate function alias binary encodings

[alexcrichton]

As-is right this red hot second the text format for the component model specifies a different binary encoding for aliasing functions from a component instance vs functions from a module instance. This difference in binary encoding, however, is not reflected in the AST or text format (they both simply use "func"). This is slated to get fixed with WebAssembly/component-model#29, however.

I'm filing this issue as a placeholder to write down in tests. Some tests that should be valid or have a different error message will instead have this error message since function aliases in wast are always encoded as core wasm function aliases instead of sometimes component function aliases.