*: 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/relay/tests/lib.rs

@@ -1147,11 +1147,12 @@ enum CombinedEvent {
 }
 
 impl CombinedBehaviour {
-    fn poll<TEv>(
+    fn poll(
         &mut self,
         _: &mut Context,
         _: &mut impl PollParameters,
-    ) -> Poll<NetworkBehaviourAction<TEv, CombinedEvent>> {
+    ) -> Poll<NetworkBehaviourAction<CombinedEvent, <Self as NetworkBehaviour>::ProtocolsHandler>>
+    {
         if !self.events.is_empty() {
             return Poll::Ready(NetworkBehaviourAction::GenerateEvent(self.events.remove(0)));
         }