crypto: DRY type checking

Factor out some common code.  The `checkUint()` function will also be
used in a follow-up commit that adds scrypt support to core.

PR-URL: https://github.com/nodejs/node/pull/20816


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>