async performStartup(e) {
    const t = this.serviceRegistry.all.flatMap((s) => s.LanguageMetaData.fileExtensions), r = [], i = (s) => {
      r.push(s), this.langiumDocuments.hasDocument(s.uri) || this.langiumDocuments.addDocument(s);
    };
    return await this.loadAdditionalDocuments(e, i), await Promise.all(e.map((s) => [s, this.getRootFolder(s)]).map(async (s) => this.traverseFolder(...s, t, i))), this._ready.resolve(), r;
  }
Performs the uninterruptable startup sequence of the workspace manager.
This methods loads all documents in the workspace and other documents and returns them.