osx: fix media keys input when other Apps steal the priority

other Apps do the same as mpv and tap into the global event chain.
events that are handled are not being propagated down the event chain.
that can lead to mpv not getting any media key events anymore when they
are held back by other Apps. we will just move mpv back to the top of
the event list when mpv is refocused and is not at the top of the list
any more.

Fixes #4834

osdep/macosx_application.m

@@ -139,6 +139,11 @@ static void terminate_cocoa_application(void)
              andEventID:kAEQuitApplication];
 }
 
+- (void)applicationWillBecomeActive:(NSNotification *)notification
+{
+    [_eventsResponder setHighestPriotityMediaKeysTap];
+}
+
 - (void)handleQuitEvent:(NSAppleEventDescriptor *)event
          withReplyEvent:(NSAppleEventDescriptor *)replyEvent
 {

osdep/macosx_events.m

@@ -372,6 +372,25 @@ void cocoa_set_mpv_handle(struct mpv_handle *ctx)
     CGEventTapEnable(self->_mk_tap_port, true);
 }
 
+- (void)setHighestPriotityMediaKeysTap
+{
+    if (self->_mk_tap_port == nil)
+        return;
+
+    CGEventTapInformation *taps = ta_alloc_size(nil, sizeof(CGEventTapInformation));
+    uint32_t numTaps = 0;
+    CGError err = CGGetEventTapList(1, taps, &numTaps);
+
+    if (err == kCGErrorSuccess && numTaps > 0) {
+        pid_t processID = [NSProcessInfo processInfo].processIdentifier;
+        if (taps[0].tappingProcess != processID) {
+            [self stopMediaKeys];
+            [self startMediaKeys];
+        }
+    }
+    talloc_free(taps);
+}
+
 - (void)startMediaKeys
 {
     dispatch_async(dispatch_get_main_queue(), ^{
@@ -396,6 +415,7 @@ void cocoa_set_mpv_handle(struct mpv_handle *ctx)
 {
     dispatch_async(dispatch_get_main_queue(), ^{
         NSMachPort *port = (NSMachPort *)self->_mk_tap_port;
+        CGEventTapEnable(self->_mk_tap_port, false);
         [[NSRunLoop mainRunLoop] removePort:port forMode:NSRunLoopCommonModes];
         CFRelease(self->_mk_tap_port);
         self->_mk_tap_port = nil;

osdep/macosx_events_objc.h

@@ -40,6 +40,8 @@ struct input_ctx;
 
 - (void)putKey:(int)keycode;
 
+- (void)setHighestPriotityMediaKeysTap;
+
 - (void)handleFilesArray:(NSArray *)files;
 
 - (bool)processKeyEvent:(NSEvent *)event;