src/vs/base/common/strings.ts/AmbiguousCharacters/intersectMaps
class AmbiguousCharacters:		function intersectMaps(
			map1: Map<number, number> | undefined,
			map2: Map<number, number>
		) {
			if (!map1) {
				return map2;
			}
			const result = new Map<number, number>();
			for (const [key, value] of map1) {
				if (map2.has(key)) {
					result.set(key, value);
				}
			}
			return result;
		}