Extended support for gpg keys

In Debian 10, by default in GnuPG, the CLI utility: gpg generates a key pair (RSA/DSA) and nothing more.

I checked the
$ john/run/gpg2john gpg_key.asc #The hash is retrieved correctly and is subject to password recovery.

But updated versions of GnuPG now generate a key pair (ECC:Curve25519) by default.

And the routine for extracting the hash is not able to extract the hash of this encryption (maybe john himself does not support this encryption format). The user will always get an error:
$ john/run/gpg2john gpg_ecc_john.asc

File gpg_ecc_john.asc
Unknown public key(pub 19)
Bad parameter: encrypted_Secret_Key(len=-1, sha1=0), len can not be negative.

Although I have Kleopatra/KDE gpg/pgp key management software installed on my Debian 10, when generating keys, it has long been possible to choose a cryptographic algorithm (not RSA/DSA), but cv25519:

I generated such key in gpg CLI on Termux under name "gpg_ecc_john.asc" password "johnjohn666" And tested it on Debian 10 it imported successfully and encrypts data.
You can practice on it (note — I’m not sure that in the Russian Federation it’s so easy for citizens to engage in cryptography and removed the link to the key.):

JtR does not fully work with GPG keys, it might be worth considering a request to support this encryption algorithm (in the future / already it will become preferable, judging by its purpose when generating keys by default).

This is a continuation from here:
https://github.com/openwall/john/issues/5252#issuecomment-1467751212

Start with the gpg2john entry point in john/run and reproduce the reported failure using gpg_ecc_john.asc or an equivalent Curve25519-generated key. Trace how the existing RSA/DSA key format is parsed and determine the required support for public key type 19. Done means the utility extracts a usable hash from the ECC key without the reported errors and covers the behavior with a regression test.