Introduce common helper functions

src/activities/settings/SettingActionDispatch.h

@@ -0,0 +1,13 @@
+#pragma once
+#include <memory>
+
+#include "SettingInfo.h"
+
+class Activity;
+class GfxRenderer;
+class MappedInputManager;
+
+// Creates the sub-activity corresponding to the given SettingAction.
+// Returns nullptr for None, Submenu, or unknown actions (caller handles those).
+std::unique_ptr<Activity> createActivityForAction(SettingAction action, GfxRenderer& renderer,
+                                                  MappedInputManager& mappedInput);