Since #12241 we have notifications for this when the user navigates away from the viewer, but we do not yet warn when switching documents, which means that if you call e.g. `PDFViewerApplication.open` with a new document (or directly call `BaseViewer.setDocument` when using the viewer components standalone) there won't be any warning about losing form data. This should be addressed.
constructor() {
    throw new Error("Cannot initialize DefaultExternalServices.");
  }
  static updateFindControlState(data) {}
  static updateFindMatchesCount(data) {}
  static initPassiveLoading(callbacks) {}
  static async fallback(data) {}
  static reportTelemetry(data) {}
  static createDownloadManager(options) {
    throw new Error("Not implemented: createDownloadManager");
  }
  static createPreferences() {
    throw new Error("Not implemented: createPreferences");
  }
  static createL10n(options) {