Refactor LegacyCallHandler event emitter to use TypedEventEmitter (#29008)

* Switch LegacyCallHandler over to TypedEventEmitter and use emits to notify consumers of protocol support updates

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

* Add test for dialpad

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

---------

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

playwright/e2e/voip/pstn.spec.ts

@@ -0,0 +1,31 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+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 { test, expect } from "../../element-web-test";
+
+test.describe("PSTN", () => {
+    test.beforeEach(async ({ page }) => {
+        // Mock the third party protocols endpoint to look like the HS has PSTN support
+        await page.route("**/_matrix/client/v3/thirdparty/protocols", async (route) => {
+            await route.fulfill({
+                status: 200,
+                json: {
+                    "im.vector.protocol.pstn": {},
+                },
+            });
+        });
+    });
+
+    test("should render dialpad as expected", { tag: "@screenshot" }, async ({ page, user, toasts }) => {
+        await toasts.rejectToast("Notifications");
+        await toasts.assertNoToasts();
+
+        await expect(page.locator(".mx_LeftPanel_filterContainer")).toMatchScreenshot("dialpad-trigger.png");
+        await page.getByLabel("Open dial pad").click();
+        await expect(page.locator(".mx_Dialog")).toMatchScreenshot("dialpad.png");
+    });
+});