[Runtime] Bound XCMP queue (#2302)

Remove `without_storage_info` from the XCMP queue pallet. Part of
https://github.com/paritytech/polkadot-sdk/issues/323

Changes:
- Limit the number of channels that can be suspended at the same time.
- Limit the number of channels that can have messages or signals pending
at the same time.

A No-OP migration is put in place to ensure that all `BoundedVec`s still
decode and not truncate after upgrade. The storage version is thereby
bumped to 4 to have our tooling remind us to deploy that migration.

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Francisco Aguirre <franciscoaguirreperez@gmail.com>

cumulus/primitives/core/src/lib.rs

@@ -64,6 +64,8 @@ pub enum MessageSendError {
 	TooBig,
 	/// Some other error.
 	Other,
+	/// There are too many channels open at once.
+	TooManyChannels,
 }
 
 impl From<MessageSendError> for &'static str {
@@ -74,6 +76,7 @@ impl From<MessageSendError> for &'static str {
 			NoChannel => "NoChannel",
 			TooBig => "TooBig",
 			Other => "Other",
+			TooManyChannels => "TooManyChannels",
 		}
 	}
 }
@@ -135,6 +138,11 @@ pub trait GetChannelInfo {
 	fn get_channel_info(id: ParaId) -> Option<ChannelInfo>;
 }
 
+/// List all open outgoing channels.
+pub trait ListChannelInfos {
+	fn outgoing_channels() -> Vec<ParaId>;
+}
+
 /// Something that should be called when sending an upward message.
 pub trait UpwardMessageSender {
 	/// Send the given UMP message; return the expected number of blocks before the message will