gtk: Check implicit grab status before sending crossing events

As we now refrain from sending the crossing events if there's an
implicit grab, those events must be sent on button release when
the implicit grab is broken.

gtk/gtkmain.c

@@ -1508,8 +1508,12 @@ handle_pointing_event (GdkEvent *event)
 
       if (event->type == GDK_MOTION_NOTIFY || event->type == GDK_ENTER_NOTIFY)
         {
-          gtk_synthesize_crossing_events (toplevel, old_target, target,
-                                          event, GDK_CROSSING_NORMAL);
+          if (!gtk_window_lookup_pointer_focus_implicit_grab (toplevel, device,
+                                                              sequence))
+            {
+              gtk_synthesize_crossing_events (toplevel, old_target, target,
+                                              event, GDK_CROSSING_NORMAL);
+            }
 
           gtk_window_maybe_update_cursor (toplevel, NULL, device);
         }
@@ -1532,7 +1536,13 @@ handle_pointing_event (GdkEvent *event)
                                          target : NULL);
 
       if (event->type == GDK_BUTTON_RELEASE)
-        gtk_window_maybe_update_cursor (toplevel, NULL, device);
+        {
+          old_target = target;
+          target = _gtk_toplevel_pick (toplevel, x, y, NULL, NULL);
+          gtk_synthesize_crossing_events (toplevel, old_target, target, event,
+                                          GDK_CROSSING_UNGRAB);
+          gtk_window_maybe_update_cursor (toplevel, NULL, device);
+        }
       break;
     case GDK_SCROLL:
     case GDK_TOUCHPAD_PINCH:

gtk/gtkwindow.c

@@ -11327,6 +11327,17 @@ gtk_window_lookup_effective_pointer_focus_widget (GtkWindow        *window,
   return focus ? gtk_pointer_focus_get_effective_target (focus) : NULL;
 }
 
+GtkWidget *
+gtk_window_lookup_pointer_focus_implicit_grab (GtkWindow        *window,
+                                               GdkDevice        *device,
+                                               GdkEventSequence *sequence)
+{
+  GtkPointerFocus *focus;
+
+  focus = gtk_window_lookup_pointer_focus (window, device, sequence);
+  return focus ? gtk_pointer_focus_get_implicit_grab (focus) : NULL;
+}
+
 void
 gtk_window_update_pointer_focus (GtkWindow        *window,
                                  GdkDevice        *device,

gtk/gtkwindowprivate.h

@@ -146,6 +146,9 @@ GtkWidget *      gtk_window_lookup_pointer_focus_widget (GtkWindow        *windo
 GtkWidget *      gtk_window_lookup_effective_pointer_focus_widget (GtkWindow        *window,
                                                                    GdkDevice        *device,
                                                                    GdkEventSequence *sequence);
+GtkWidget *      gtk_window_lookup_pointer_focus_implicit_grab (GtkWindow        *window,
+                                                                GdkDevice        *device,
+                                                                GdkEventSequence *sequence);
 
 void             gtk_window_update_pointer_focus (GtkWindow        *window,
                                                   GdkDevice        *device,