Return true if the type of x is instance of ctor.

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.InstanceOf(Date);
const a: unknown = new Date();
if (isMyType(a)) {
  // a is narrowed to Date
  const _: Date = a;
}