DDSSEC11 — Normative IDL does not match the documentation for Auth::validate_remote_identity

In the normative IDL, validate_remote_identity's signature suggests it receives IdentityHandles for the initiator of and the replier to a handshake.
This implies that this has been resolved by the middleware before calling Auth to initiate the sequence.
In the specification document, however, the function instead receives IdentityHandles for the local and remote principal, moving the resolution to the plugin.
The latter makes more sense, but to enforce this specification of the interface, the IDL has to be altered.

Fix validate_remote_identity on IDL and Document to be Consistent

This will apply the changes described in DDSSEC11-21