A pallet which uses the XCMP transport layer to handle both incoming and outgoing XCM message sending and dispatch, queuing, signalling and backpressure. To do so, it implements:
XcmpMessageHandlerXcmpMessageSource
Also provides an implementation of SendXcm which can be placed in a router tuple for relaying
XCM over XCMP if the destination is Parent/Parachain. It requires an implementation of
XcmExecutor for dispatching incoming XCM messages.