Re: [PATCH] fsmonitor: eliminate call to deprecated FSEventStream function

> From: Jeff Hostetler <jeffhostetler@github.com>
>
> Replace the call to `FSEventStreamScheduleWithRunLoop()` function with
> the suggested `FSEventStreamSetDispatchQueue()` function.
>
> The MacOS version of the builtin FSMonitor feature uses the
> `FSEventStreamScheduleWithRunLoop()` function to drive the event loop
> and process FSEvents from the system.  This routine has now been
> deprecated by Apple.  The MacOS 13 (Ventana) compiler tool chain now
> generates a warning when compiling calls to this function.  In
> DEVELOPER=1 mode, this now causes a compile error.
>
> The `FSEventStreamSetDispatchQueue()` function is conceptually similar
> and is the suggested replacement.  However, there are some subtle
> thread-related differences.
>
> Previously, the event stream would be processed by the
> `fsm_listen__loop()` thread while it was in the `CFRunLoopRun()`
> method.  (Conceptually, this was a blocking call on the lifetime of
> the event stream where our thread drove the event loop and individual
> events were handled by the `fsevent_callback()`.)
>
> With the change, a "dispatch queue" is created and FSEvents will be
> processed by a hidden queue-related thread (that calls the
> `fsevent_callback()` on our behalf).  Our `fsm_listen__loop()` thread
> maintains the original blocking model by waiting on a mutex/condition
> variable pair while the hidden thread does all of the work.