True if maybeIndexed is a Collection.Indexed, or any of its subclasses.
isIndexed(maybeIndexed: unknown): boolean
const { isIndexed, Map, List, Stack, Set } = require('immutable');
isIndexed([]); // false
isIndexed({}); // false
isIndexed(Map()); // false
isIndexed(List()); // true
isIndexed(Stack()); // true
isIndexed(Set()); // falserun it