compat/fsmonitor/fsm-listen-darwin: implement FSEvent listener on MacOS

Implement file system event listener on MacOS using FSEvent,
CoreFoundation, and CoreServices.

Co-authored-by: Kevin Willford <[email protected]>
Co-authored-by: Johannes Schindelin <[email protected]>
Signed-off-by: Jeff Hostetler <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: 3 people