Build with latest TS nightly (#120690)

* Pick up new TS 4.3

Also tests adding override keywords for extensions as part of #120675

* Update to daily TS and workaround TS 4.3 issue

Works around https://github.com/microsoft/TypeScript/issues/43578

extensions/simple-browser/src/simpleBrowserView.ts

@@ -72,7 +72,7 @@ export class SimpleBrowserView extends Disposable {
 		this.show(url);
 	}
 
-	public dispose() {
+	public override dispose() {
 		this._onDidDispose.fire();
 		super.dispose();
 	}