Move ToastContext and utilities to shared components (#33949)

* Move ToastContext and utilities to shared components

* lint

* fix type

* cleanup

* fix broken test

* fix lint

* Add more tests for ToastContext

* Potential fix for pull request finding 'Unused variable, import, function or class'

Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

---------

Co-authored-by: Copilot Autofix powered by AI <223894421+github-code-quality[bot]@users.noreply.github.com>

apps/web/test/unit-tests/contexts/ToastContext-test.ts

@@ -1,35 +0,0 @@
-/*
-Copyright 2024 New Vector Ltd.
-Copyright 2024 The Matrix.org Foundation C.I.C.
-
-SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
-Please see LICENSE files in the repository root for full details.
-*/
-
-import { ToastRack } from "../../../src/contexts/ToastContext";
-
-describe("ToastRack", () => {
-    it("should return a toast once one is displayed", () => {
-        const toastRack = new ToastRack();
-        toastRack.displayToast("Hello, world!");
-
-        expect(toastRack.getActiveToast()).toBe("Hello, world!");
-    });
-
-    it("calls update callback when a toast is added", () => {
-        const toastRack = new ToastRack();
-        const updateCallbackFn = jest.fn();
-        toastRack.setCallback(updateCallbackFn);
-        toastRack.displayToast("Hello, world!");
-
-        expect(updateCallbackFn).toHaveBeenCalled();
-    });
-
-    it("removes toast when remove function is called", () => {
-        const toastRack = new ToastRack();
-        const removeFn = toastRack.displayToast("Hello, world!");
-        expect(toastRack.getActiveToast()).toBe("Hello, world!");
-        removeFn();
-        expect(toastRack.getActiveToast()).toBeUndefined();
-    });
-});