Centralize calling toasts and add imperative API

ts/hooks/useIsMounted.ts

@@ -0,0 +1,28 @@
+// Copyright 2023 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { useCallback, useEffect, useRef } from 'react';
+
+/**
+ * If you get a warning like:
+ *
+ * Warning: Can't perform a React state update on an unmounted component.
+ *
+ * your component is probably trying to set state after it has unmounted, e.g. after a
+ * timeout or async call. If you can, clear the timeout when the component unmounts (e.g.
+ * on useEffect cleanup). Otherwise, use this hook to check if the component is mounted
+ * before updating state.
+ */
+
+export function useIsMounted(): () => boolean {
+  const isMounted = useRef(false);
+
+  useEffect(() => {
+    isMounted.current = true;
+    return () => {
+      isMounted.current = false;
+    };
+  }, []);
+
+  return useCallback(() => isMounted.current === true, []);
+}