Add ReadonlyMap and ReadonlySet as Serializable

[bjohn465]

The Serializable type currently defines Maps and Sets as serializable if their keys and/or values are serializable (see https://github.com/remix-run/react-router/blob/ab67e21/packages/react-router/lib/server-runtime/single-fetch.ts#L298-L299).

The Serialize type is similar, but serializes types that extend Map or Set, rather than types that are Maps or Sets (see https://github.com/remix-run/react-router/blob/ab67e21/packages/react-router/lib/types/route-data.ts#L23-L24).

ReadonlyMap and ReadonlySet are separate types that do not extend Map or Set, but they are subsets of Map and Set that only define the non-mutating methods.

Since ReadonlyMap and ReadonlySet aren't Map and Set and do not extend Map and Set, they do not serialize correctly (as a type, that is). Since they are Typescript-only types (in that you can't create a ReadonlyMap or ReadonlySet object), they should serialize exactly like Map and Set.

I propose that Serializable, Serialize, and any other types as needed be updated to support serializing ReadonlyMap and ReadonlySet so that code such as useLoaderData will keep ReadonlyMap and ReadonlySet types.

[bjohn465]

Here's a repository with an example: https://github.com/bjohn465/readonly-example

Currently, TypeScript throws an error on line 61 and line 67 because the ReadonlyMap and ReadonlySet types are not serialized correctly. The readonlyMap and readonlySet items in the loader data and action data do come across correctly as a Map and Set, though.

[bjohn465]

A failing test was submitted in this PR: #13092