Stop relying on `@_distributedActorIndependent` anywhere.
This is an non-user-visible attribute that is semantically identical to
`nonisolated` except that it allows use in distributed actors. It is
only, and can only, be used for the two fields that distributed actors
have in both the local actor and in the remote proxy, "id" and
"actorTransport". So, special-case the "nonisolated" check for those
fields and stop using `@_distributedActorIndependent`.
