doc: document ABORT_ERR code

We added an `AbortError` with the same code and name as the web's as
part of the consensus in https://github.com/nodejs/node/issues/36084 but
never actually documented the error in our error codes list.

This PR adds the error code.

PR-URL: https://github.com/nodejs/node/pull/36319


Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>