WiiTASInputWindow: Update controls when attachment changes

Change the displayed controls in the TAS Input window when the
controller's extension (including MotionPlus) is changed.

This previously required restarting Dolphin after the attachment was
changed, as the controls were never updated after the WiiTASInputWindow
was created at Dolphin startup.

Source/Core/InputCommon/ControllerEmu/ControlGroup/Attachments.cpp

@@ -35,6 +35,11 @@ NumericSetting<int>& Attachments::GetSelectionSetting()
   return m_selection_setting;
 }
 
+SubscribableSettingValue<int>& Attachments::GetAttachmentSetting()
+{
+  return m_selection_value;
+}
+
 const std::vector<std::unique_ptr<EmulatedController>>& Attachments::GetAttachmentList() const
 {
   return m_attachments;