[core/swarm] Emit events for active connection close and fix disconnect(). (#1619)

* Emit events for active connection close and fix `disconnect()`.

The `Network` does currently not emit events for actively
closed connections, e.g. via `EstablishedConnection::close`
or `ConnectedPeer::disconnect()`. As a result, when actively
closing connections, there will be `ConnectionEstablished`
events emitted without eventually a matching `ConnectionClosed`
event. This seems undesirable and has the consequence that
the `Swarm::ban_peer_id` feature in `libp2p-swarm` does not
result in appropriate calls to `NetworkBehaviour::inject_connection_closed`
and `NetworkBehaviour::inject_disconnected`. Furthermore,
the `disconnect()` functionality in `libp2p-core` is currently
broken as it leaves the `Pool` in an inconsistent state.

This commit does the following:

  1. When connection background tasks are dropped
     (i.e. removed from the `Manager`), they
     always terminate immediately, without attempting
     an orderly close of the connection.
  2. An orderly close is sent to the background task
     of a connection as a regular command. The
     background task emits a `Closed` event
     before terminating.
  3. `Pool::disconnect()` removes all connection
     tasks for the affected peer from the `Manager`,
     i.e. without an orderly close, thereby also
     fixing the discovered state inconsistency
     due to not removing the corresponding entries
     in the `Pool` itself after removing them from
     the `Manager`.
  4. A new test is added to `libp2p-swarm` that
     exercises the ban/unban functionality and
     places assertions on the number and order
     of calls to the `NetworkBehaviour`. In that
     context some new testing utilities have
     been added to `libp2p-swarm`.

This addresses https://github.com/libp2p/rust-libp2p/issues/1584.

* Update swarm/src/lib.rs

Co-authored-by: Toralf Wittner <tw@dtex.org>

* Incorporate some review feedback.

* Adapt to changes in master.

* More verbose panic messages.

* Simplify

There is no need for a `StartClose` future.

* Fix doc links.

* Further small cleanup.

* Update CHANGELOGs and versions.

Co-authored-by: Toralf Wittner <tw@dtex.org>

swarm/src/protocols_handler/dummy.rs

@@ -31,12 +31,15 @@ use std::task::{Context, Poll};
 use void::Void;
 
 /// Implementation of `ProtocolsHandler` that doesn't handle anything.
+#[derive(Clone, Debug)]
 pub struct DummyProtocolsHandler {
+    pub keep_alive: KeepAlive,
 }
 
 impl Default for DummyProtocolsHandler {
     fn default() -> Self {
         DummyProtocolsHandler {
+            keep_alive: KeepAlive::No
         }
     }
 }
@@ -49,19 +52,16 @@ impl ProtocolsHandler for DummyProtocolsHandler {
     type OutboundProtocol = DeniedUpgrade;
     type OutboundOpenInfo = Void;
 
-    #[inline]
     fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(DeniedUpgrade)
     }
 
-    #[inline]
     fn inject_fully_negotiated_inbound(
         &mut self,
         _: <Self::InboundProtocol as InboundUpgrade<NegotiatedSubstream>>::Output
     ) {
     }
 
-    #[inline]
     fn inject_fully_negotiated_outbound(
         &mut self,
         _: <Self::OutboundProtocol as OutboundUpgrade<NegotiatedSubstream>>::Output,
@@ -69,16 +69,14 @@ impl ProtocolsHandler for DummyProtocolsHandler {
     ) {
     }
 
-    #[inline]
     fn inject_event(&mut self, _: Self::InEvent) {}
 
-    #[inline]
     fn inject_dial_upgrade_error(&mut self, _: Self::OutboundOpenInfo, _: ProtocolsHandlerUpgrErr<<Self::OutboundProtocol as OutboundUpgrade<NegotiatedSubstream>>::Error>) {}
 
-    #[inline]
-    fn connection_keep_alive(&self) -> KeepAlive { KeepAlive::No }
+    fn connection_keep_alive(&self) -> KeepAlive {
+        self.keep_alive
+    }
 
-    #[inline]
     fn poll(
         &mut self,
         _: &mut Context<'_>,