Use FSEvents in wxFileSystemWatcher on OS X

The FSEvents API allows for creating watches in entire trees of
directories in an efficient manner.

Closes #16969.

include/wx/osx/cocoa/chkconf.h

@@ -50,6 +50,16 @@
 #define wxOSX_USE_QUICKTIME 0
 #define wxOSX_USE_AUDIOTOOLBOX 1
 
+/*
+   Use the more efficient FSEvents API instead of kqueue
+   events for file system watcher, but only on OS X >= 10.7 since
+   that version introduced a flag that allows watching files as
+   well as sub directories.
+ */
+#if MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_7
+    #define wxHAVE_FSEVENTS_FILE_NOTIFICATIONS 1
+#endif
+
 /*
  * turning off capabilities that don't work under cocoa yet
  */