Only reset tooltip timer when mouse actually moved

InputEventMouseMotion isn't guaranteed to fire only on actual mouse
movement. It's not uncommon for the underlying OS motion event to be
sent either by the OS itself or another application even though the
mouse hasn't moved.  Godot will generate such zero-motion
InputEventMouseMotion events itself for things like cursor shape
changes.

Once started, the tooltip timer is reset only after a mouse movement of
at least 5 pixels in one frame.

scene/main/viewport.cpp

@@ -1933,7 +1933,12 @@ void Viewport::_gui_input_event(Ref<InputEvent> p_event) {
 					}
 				}
 
-				if (!is_tooltip_shown && over->can_process()) {
+				// If the tooltip timer isn't running, start it.
+				// Otherwise, only reset the timer if the mouse has moved more than 5 pixels.
+				if (!is_tooltip_shown && over->can_process() &&
+						(gui.tooltip_timer.is_null() ||
+								Math::is_zero_approx(gui.tooltip_timer->get_time_left()) ||
+								mm->get_relative().length() > 5.0)) {
 					if (gui.tooltip_timer.is_valid()) {
 						gui.tooltip_timer->release_connections();
 						gui.tooltip_timer = Ref<SceneTreeTimer>();