Previously we would not propagate those into the generated distributed
actor, making a lot of generic distributed actor protocols impossible to
express.
We indeed cannot handle protocols WITHOUT primary associated types, but
we certainly can handle them with!
This resolves rdar://139332556
The macro cannot diagnose some situations, or rather, would diagnose too
aggressively, because it cannot inspect the type declarations of all
invokved types, and therefore we're unable to reliably report errors
only when necessary.
Originally I thought we don't want to emit macro code that "may fail to
compile" but we don't really have a choice.
This patch removes a manual diagnostic, and enables more correct code to
properly use @Resolvable protocols.
