src/vs/editor/common/languages/supports/richEditBrackets.ts/unique
function unique(arr: string[]): string[] {
	if (arr.length <= 1) {
		return arr;
	}
	const result: string[] = [];
	const seen = new Set<string>();
	for (const element of arr) {
		if (seen.has(element)) {
			continue;
		}
		result.push(element);
		seen.add(element);
	}
	return result;
}