src/vs/workbench/api/browser/mainThreadCustomEditors.ts/MainThreadCustomEditorModel/suggestUntitledSavePath
class MainThreadCustomEditorModel:	private suggestUntitledSavePath(options: ISaveOptions | undefined): Promise<URI | undefined> {
		if (!this.isUntitled()) {
			throw new Error('Resource is not untitled');
		}

		const remoteAuthority = this._environmentService.remoteAuthority;
		const localResource = toLocalResource(this._editorResource, remoteAuthority, this._pathService.defaultUriScheme);

		return this._fileDialogService.pickFileToSave(localResource, options?.availableFileSystems);
	}