`instanceof AjaxError` no longer possible since 7.0.0-rc.0

[OliverJAsh]

Bug Report

Current Behavior
In 7.0.0-beta.15 this did not error.

In 7.0.0-rc.0 and above, this results in an error.

import { AjaxError } from 'rxjs/ajax';
declare const error: unknown;
// Error:
// The right-hand side of an 'instanceof' expression must be of type 'any' or of a type assignable to the 'Function' interface type.
error instanceof AjaxError;

Expected behavior
No error

---

I glanced at the changelog but nothing stood out: https://github.com/ReactiveX/rxjs/blob/master/CHANGELOG.md#700-rc0-2021-04-19.

[voliva]

I've found the source of this issue: AjaxErrorCtor signature is marked as @internal, and now the build step removes it.

I'll raise a PR now with a posible fix

[cartant]

Closed by #6275