Return an Readonly annotated type predicate function that returns true if the type of x is T.

This is unstable and may be removed in the future.

Note that this function does nothing but annotate the predicate function as Readonly.

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.ReadonlyOf(is.TupleOf([is.String, is.Number]));
const a: unknown = ["a", 1];
if (isMyType(a)) {
  // a is narrowed to readonly [string, number]
  const _: readonly [string, number] = a;
}