Show tooltips on narrow tabbed views (#12624)

* Show tooltips on narrow tabbed views

* Also only show on left-side tabs

* Unused import

* Comments

* Add test

* More test

* Assert tooltip appears in playwright test

src/hooks/useWindowWidth.ts

@@ -0,0 +1,42 @@
+/*
+Copyright 2024 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import React from "react";
+
+import UIStore, { UI_EVENTS } from "../stores/UIStore";
+
+/**
+ * Hook that gets the width of the viewport using UIStore
+ *
+ * @returns the current window width
+ */
+export const useWindowWidth = (): number => {
+    const [width, setWidth] = React.useState(UIStore.instance.windowWidth);
+
+    React.useEffect(() => {
+        UIStore.instance.on(UI_EVENTS.Resize, () => {
+            setWidth(UIStore.instance.windowWidth);
+        });
+
+        return () => {
+            UIStore.instance.removeListener(UI_EVENTS.Resize, () => {
+                setWidth(UIStore.instance.windowWidth);
+            });
+        };
+    }, []);
+
+    return width;
+};