Merge PR #22555 into master

* refs/pull/22555/head:
	msg: define MFoo::create helper
	msg: add msgref cast method
	msg: cleanup factory/ref definition in messages
	mds: use message factory to avoid leaks
	msg: add factory method to correctly construct smart_ptr
	mds: remove dead MDS-MDS forwarding code
	mds: manage Message lifetime with intrusive_ptr
	common: add templated Context factory
	msg: add const version of get_payload
	msg: use queue of messages for dispatch
	msg: dispatch intrusive_ptr Messages
	msg: use deque for dispatcher pointers

Reviewed-by: Zheng Yan <zyan@redhat.com>