function mergeEnvironmentFlags(flags) {
	if (!process.env.ESLINT_FLAGS) {
		return flags;
	}

	const envFlags = process.env.ESLINT_FLAGS.trim().split(/\s*,\s*/gu);
	return Array.from(new Set([...envFlags, ...flags]));
}
Retrieves flags from the environment variable ESLINT_FLAGS.
@param {string[]} flags The flags defined via the API.
@returns {string[]} The merged flags to use.