Return a type predicate function that returns true if the type of x is Set<T>.

To enhance performance, users are advised to cache the return value of this function and mitigate the creation cost.

import { is } from "@core/unknownutil";

const isMyType = is.SetOf(is.String);
const a: unknown = new Set(["a", "b", "c"]);
if (isMyType(a)) {
  // a is narrowed to Set<string>
  const _: Set<string> = a;
}