Implement Network Bridge (#1280)

* network bridge skeleton

* move some primitives around and add debug impls

* protocol registration glue & abstract network interface

* add send_msgs to subsystemctx

* select logic

* transform different events into actions and handle

* implement remaining network bridge state machine

* start test skeleton

* make network methods asynchronous

* extract subsystem out to subsystem crate

* port over overseer to subsystem context trait

* fix minimal example

* fix overseer doc test

* update network-bridge crate

* write a subsystem test-helpers crate

* write a network test helper for network-bridge

* set up (broken) view test

* Revamp network to be more async-friendly and not require Sync

* fix spacing

* fix test compilation

* insert side-channel for actions

* Add some more message types to AllMessages

* introduce a test harness

* add some tests

* ensure service compiles and passes tests

* fix typo

* fix service-new compilation

* Subsystem test helpers send messages synchronously

* remove smelly action inspector

* remove superfluous let binding

* fix warnings

* Update node/network/bridge/src/lib.rs

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* fix compilation

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

polkadot/node/primitives/src/lib.rs

@@ -64,6 +64,7 @@ impl EncodeAs<CompactStatement> for Statement {
 pub type SignedFullStatement = Signed<Statement, CompactStatement>;
 
 /// A misbehaviour report.
+#[derive(Debug)]
 pub enum MisbehaviorReport {
 	/// These validator nodes disagree on this candidate's validity, please figure it out
 	///
@@ -79,3 +80,12 @@ pub enum MisbehaviorReport {
 	/// This peer has seconded more than one parachain candidate for this relay parent head
 	DoubleVote(CandidateReceipt, SignedFullStatement, SignedFullStatement),
 }
+
+/// A unique identifier for a network protocol.
+pub type ProtocolId = [u8; 4];
+
+/// A succinct representation of a peer's view. This consists of a bounded amount of chain heads.
+///
+/// Up to `N` (5?) chain heads.
+#[derive(Debug, Clone, PartialEq, Eq, Encode, Decode)]
+pub struct View(pub Vec<Hash>);