Clear settings store cache on logout (#12786)

And clear it in the widget layout store test, also fixing the tests
which didn't actually individually as they actually relied on the state
bleeding between tests.

src/Lifecycle.ts

@@ -1056,6 +1056,7 @@ export async function onLoggedOut(): Promise<void> {
     await clearStorage({ deleteEverything: true });
     LifecycleCustomisations.onLoggedOutAndStorageCleared?.();
     await PlatformPeg.get()?.clearStorage();
+    SettingsStore.reset();
 
     // Do this last, so we can make sure all storage has been cleared and all
     // customisations got the memo.