Some simple initial tests for MediaView (#2813)

* Some simple tests for MediaView

* Use jest-dom assertions

* Add tests for videoMuted

* Add test case for placeholder video track

* Revert yarn.lock changes

* More revert

* Deduplicate test case logic and improve names

* Use role and label

src/vitest.setup.ts

@@ -15,6 +15,7 @@ import { afterEach } from "vitest";
 import { cleanup } from "@testing-library/react";
 import "vitest-axe/extend-expect";
 import { logger } from "matrix-js-sdk/src/logger";
+import "@testing-library/jest-dom/vitest";
 
 import EN_GB from "../locales/en-GB/app.json";
 import { Config } from "./config/Config";