Convert Notifier to typescript

src/@types/global.d.ts

@@ -26,6 +26,7 @@ import RoomListLayoutStore from "../stores/room-list/RoomListLayoutStore";
 import {IntegrationManagers} from "../integrations/IntegrationManagers";
 import {ModalManager} from "../Modal";
 import SettingsStore from "../settings/SettingsStore";
+import {Notifier} from "../Notifier";
 
 declare global {
     interface Window {
@@ -45,6 +46,7 @@ declare global {
         mxIntegrationManagers: typeof IntegrationManagers;
         singletonModalManager: ModalManager;
         mxSettingsStore: SettingsStore;
+        mxNotifier: typeof Notifier;
     }
 
     // workaround for https://github.com/microsoft/TypeScript/issues/30933
@@ -77,4 +79,8 @@ declare global {
     interface PromiseConstructor {
         allSettled<T>(promises: Promise<T>[]): Promise<Array<ISettledFulfilled<T> | ISettledRejected>>;
     }
+
+    interface HTMLAudioElement {
+        type?: string;
+    }
 }