findConfigFile(filePath) {
		const options = privateMembers.get(this).options;

		/*
		 * Because the new config lookup scheme skips the current directory
		 * and looks into the parent directories, we need to use a placeholder
		 * directory to ensure the file in cwd is checked.
		 */
		const fakeCwd = path.join(options.cwd, "__placeholder__");

		return this.#configLoader
			.findConfigFileForPath(filePath ?? fakeCwd)
			.catch(() => void 0);
	}
Finds the config file being used by this instance based on the options
passed to the constructor.
@param {string} [filePath] The path of the file to find the config file for.
@returns {Promise<string|undefined>} The path to the config file being used or
     `undefined` if no config file is being used.