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

test/hooks/useWindowWidth-test.ts

@@ -0,0 +1,44 @@
+/*
+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 { renderHook } from "@testing-library/react-hooks";
+import { act } from "@testing-library/react";
+
+import UIStore, { UI_EVENTS } from "../../src/stores/UIStore";
+import { useWindowWidth } from "../../src/hooks/useWindowWidth";
+
+describe("useWindowWidth", () => {
+    beforeEach(() => {
+        UIStore.instance.windowWidth = 768;
+    });
+
+    it("should return the current width of window, according to UIStore", () => {
+        const { result } = renderHook(() => useWindowWidth());
+
+        expect(result.current).toBe(768);
+    });
+
+    it("should update the value when UIStore's value changes", () => {
+        const { result } = renderHook(() => useWindowWidth());
+
+        act(() => {
+            UIStore.instance.windowWidth = 1024;
+            UIStore.instance.emit(UI_EVENTS.Resize);
+        });
+
+        expect(result.current).toBe(1024);
+    });
+});