text: Ignore synthetic motion events

We want to re-show the obscured mouse cursor when the
user interacts with the mouse, not when the pointer position
relative to the widget changed. So, ignore synthetic
motion events.

Fixes: #3792

gtk/gtktext.c

@@ -2940,6 +2940,11 @@ gtk_text_motion_controller_motion (GtkEventControllerMotion *controller,
                                    GtkText                  *self)
 {
   GtkTextPrivate *priv = gtk_text_get_instance_private (self);
+  GdkEvent *event;
+
+  event = gtk_event_controller_get_current_event (GTK_EVENT_CONTROLLER (controller));
+  if (gdk_motion_event_is_synthetic (event))
+    return;
 
   if (priv->mouse_cursor_obscured)
     {

gtk/gtktextview.c

@@ -5712,6 +5712,12 @@ gtk_text_view_motion (GtkEventController *controller,
                       double              y,
                       gpointer            user_data)
 {
+  GdkEvent *event;
+
+  event = gtk_event_controller_get_current_event (GTK_EVENT_CONTROLLER (controller));
+  if (gdk_motion_event_is_synthetic (event))
+    return;
+
   gtk_text_view_unobscure_mouse_cursor (GTK_TEXT_VIEW (user_data));
 }