CDRIVER-4617 Refactor libmongoc to use mcd-rpc (#1307)

* Add mcd_rpc_message ingress/egress counter functions

* Add mcd_rpc_message compression functions

* Add mcd_rpc_message_get_body

* Add mcd_rpc_message_check_ok

* Refactor mongoc_cluster_t::request_id from uint32_t -> int32_t

* Refactor mock server to use mcd-rpc

* Refactor server monitor thread to use mcd-rpc

* Refactor mongoc-async-cmd to use mcd-rpc

* Refactor mongoc_cluster_run_command_opquery to use mcd-rpc

* Refactor mongoc_cluster_run_opmsg to use mcd-rpc

* Refactor cursor functions to use mcd-rpc

* CDRIVER-4625 Address distinct pointer type warnings on Windows

* Clean up mock server functions