Fixes a crash in xcb thunks since more stuff on FEX side has moved over
to jemalloc.
Destructors don't actually get called when a shared library is removed.
It's some weirdo quirk that we can't work around. Instead refcount
Display connections being created and disconnected. Creating the thread
on the first display creation, and tearing down on final display
teardown.
Must be merged before #2564 otherwise that PR will break thunks.
Notably, xcb_take_socket uses the callback_guest annotation, since the
given callback is never called on the host (instead it's manually forwarded
back to a helper guest thread for calling).
Ryan Houdek