Use prefixed versions of other fullscreen APIs too

src/@types/global.d.ts

@@ -17,6 +17,12 @@ limitations under the License.
 import "matrix-js-sdk/src/@types/global";
 
 declare global {
+  interface Document {
+    // Safari only supports this prefixed, so tell the type system about it
+    webkitExitFullscreen: () => void;
+    webkitFullscreenElement: HTMLElement | null;
+  }
+
   interface Window {
     // TODO: https://gitlab.matrix.org/matrix-org/olm/-/issues/10
     OLM_OPTIONS: Record<string, string>;