textinputv2: announce the input panel to be hidden as the instance gets disabled

Otherwise we disable it and all events will be disabled (since surface
gets cleared).
This is especially useful since otherwise we lose synchronicity with the
client and weird behaviours happen (like when the client thinks it has a
keyboard but it actually does not).

src/wayland/textinput_v2_interface.cpp

@@ -293,6 +293,9 @@ void TextInputV2InterfacePrivate::zwp_text_input_v2_disable(Resource *resource,
 {
     Q_UNUSED(resource)
     Q_UNUSED(s)
+
+    q->setInputPanelState(false, {0, 0, 0, 0});
+
     surface.clear();
     enabled = false;
     emit q->enabledChanged();