polywrap_native URI resolution is broken due to missing constructors

[krisbitney]

With the recent changes to the polywrap_native Rust package, it's no longer possible for users to implement a custom URI resolver because they can't construct an FfiUriPackageOrWrapper object and the callback interface for UriPackageOrWrapper was removed.

interface FFIUriPackageOrWrapper {
  FFIUriPackageOrWrapperKind get_kind();
  [Throws=FFIError]
  FFIUri as_uri();
  [Throws=FFIError]
  FFIUriWrapper as_wrapper();
  [Throws=FFIError]
  FFIUriWrapPackage as_package();
};

We also have two FfiUriResolver concepts:

callback interface IFFIUriResolver {
  [Throws=FFIError]
  FFIUriPackageOrWrapper try_resolve_uri(FFIUri uri, FFIInvoker invoker, FFIUriResolutionContext resolution_context);
};

interface FFIUriResolver {
  [Throws=FFIError]
  FFIUriPackageOrWrapper try_resolve_uri(FFIUri uri, FFIInvoker invoker, FFIUriResolutionContext resolution_context);
};

One is a class that has no constructor, but that is needed to construct FfiRecursiveUriResolver and FfiStaticUriResolver. The other is a callback interface that is not used anywhere.