*: 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>

swarm/src/protocols_handler/select.rs

@@ -45,6 +45,10 @@ impl<TProto1, TProto2> IntoProtocolsHandlerSelect<TProto1, TProto2> {
     pub(crate) fn new(proto1: TProto1, proto2: TProto2) -> Self {
         IntoProtocolsHandlerSelect { proto1, proto2 }
     }
+
+    pub fn into_inner(self) -> (TProto1, TProto2) {
+        (self.proto1, self.proto2)
+    }
 }
 
 impl<TProto1, TProto2> IntoProtocolsHandler for IntoProtocolsHandlerSelect<TProto1, TProto2>
@@ -87,6 +91,10 @@ impl<TProto1, TProto2> ProtocolsHandlerSelect<TProto1, TProto2> {
     pub(crate) fn new(proto1: TProto1, proto2: TProto2) -> Self {
         ProtocolsHandlerSelect { proto1, proto2 }
     }
+
+    pub fn into_inner(self) -> (TProto1, TProto2) {
+        (self.proto1, self.proto2)
+    }
 }
 
 impl<TProto1, TProto2> ProtocolsHandler for ProtocolsHandlerSelect<TProto1, TProto2>