cocoa: fix mouse hiding with launchpad and dock folders

Some UI elements in OS X – like Launchpad and Dock folders – are implemented
using borderless windows in background demonized applications.
When we use these elements, mpv doesn't stop to be the active application, but
the mpv window leaves keyWindow state while we use the OS controls.

This commit just keeps track of window state to update the cursor visibility
accordingly.

Fixes #513

video/out/cocoa/mpvadapter.h

@@ -28,6 +28,7 @@
 - (void)handleFilesArray:(NSArray *)files;
 - (void)didChangeWindowedScreenProfile:(NSScreen *)screen;
 - (void)performAsyncResize:(NSSize)size;
+- (void)didChangeMousePosition;
 
 - (BOOL)isInFullScreenMode;
 - (BOOL)keyboardEnabled;

video/out/cocoa/window.m

@@ -61,6 +61,16 @@
     [self.adapter didChangeWindowedScreenProfile:[self screen]];
 }
 
+- (void)windowDidResignKey:(NSNotification *)notification
+{
+    [self.adapter didChangeMousePosition];
+}
+
+- (void)windowDidBecomeKey:(NSNotification *)notification
+{
+    [self.adapter didChangeMousePosition];
+}
+
 - (BOOL)canBecomeMainWindow { return YES; }
 - (BOOL)canBecomeKeyWindow { return YES; }
 - (BOOL)windowShouldClose:(id)sender

video/out/cocoa_common.m

@@ -258,7 +258,7 @@ static int vo_cocoa_set_cursor_visibility(struct vo *vo, bool *visible)
 
     if (*visible) {
         CGDisplayShowCursor(kCGDirectMainDisplay);
-    } else if ([v canHideCursor]) {
+    } else if ([v canHideCursor] && [s->window isKeyWindow]) {
         CGDisplayHideCursor(kCGDirectMainDisplay);
     } else {
         *visible = true;
@@ -847,4 +847,10 @@ int vo_cocoa_control(struct vo *vo, int *events, int request, void *arg)
     struct vo_cocoa_state *s = self.vout->cocoa;
     s->pending_events |= VO_EVENT_ICC_PROFILE_CHANGED;
 }
+
+- (void)didChangeMousePosition
+{
+    struct vo_cocoa_state *s = self.vout->cocoa;
+    [(MpvEventsView *)s->view signalMousePosition];
+}
 @end