Add interface version support

[dicej]

Per https://github.com/WebAssembly/component-model/blob/main/design/mvp/WIT.md#package-declaration, if the WIT interface has an interface, it needs to be encoded in the component type identifier for that interface.

[dicej]

This is mostly addressed by #43, except that you can't import or export two versions of the same interface yet. We can address that as part of #21, though so I'm closing this.