Add support for aspect-oriented interceptors

[markfisher]

This should include dynamic generation of a Wasm component with the following shape:

world interceptor {
  export some-target;
  import some-target;
  import generic-advice;
}

The advice world would export an interface with an invocation resource, having a constructor and a before() and after(), each returning an "action" variant type to proceed/skip/error if before or accept/repeat/error if after.

The generated interceptor will invoke the advice as well as the target according to those actions.

This should be implemented in a separate crate within the project for now. It will likely drive some changes to the way interceptors can be configured in the TOML files.