*: Dial with handler and return handler on error and closed (#2191)

Require `NetworkBehaviourAction::{DialPeer,DialAddress}` to contain a
`ProtocolsHandler`. This allows a behaviour to attach custom state to its
handler. The behaviour would no longer need to track this state separately
during connection establishment, thus reducing state required in a behaviour.
E.g. in the case of `libp2p-kad` the behaviour can include a `GetRecord` request
in its handler, or e.g. in the case of `libp2p-request-response` the behaviour
can include the first request in the handler.

Return `ProtocolsHandler` on connection error and close. This allows a behaviour
to extract its custom state previously included in the handler on connection
failure and connection closing. E.g. in the case of `libp2p-kad` the behaviour
could extract the attached `GetRecord` from the handler of the failed connection
and then start another connection attempt with a new handler with the same
`GetRecord` or bubble up an error to the user.

Co-authored-by: Thomas Eizinger <thomas@eizinger.io>

protocols/mdns/src/behaviour.rs

@@ -287,12 +287,7 @@ impl NetworkBehaviour for Mdns {
         &mut self,
         cx: &mut Context<'_>,
         params: &mut impl PollParameters,
-    ) -> Poll<
-        NetworkBehaviourAction<
-            <Self::ProtocolsHandler as ProtocolsHandler>::InEvent,
-            Self::OutEvent,
-        >,
-    > {
+    ) -> Poll<NetworkBehaviourAction<Self::OutEvent, DummyProtocolsHandler>> {
         while let Poll::Ready(event) = Pin::new(&mut self.if_watch).poll(cx) {
             let socket = self.recv_socket.get_ref();
             match event {