PGSC: Add JCE implementation for OpenPGP Smart Card message decryption

[vanitasvitae]

This PR is based on and includes #2339

Inhere, I modified BCs API to allow for message decryption with external secret keys.
On top of that, I introduced AbstractPublicKeyDataDecryptorFactory.getCryptoCallback() and reworked the BcPublicKeyDataDecryptorFactory to cleanly separate out PK crypto operations during session-key recovery, for sake of simple delegation to hardware devices in subclasses.

Furthermode, the new module pgsc now contains the initial design of a smart card API for bcpg. It currently supports listing cards, uploading key material and decrypting messages using both a simulated smart card backend, as well as an implementation using the YubiKit library.

TODO:

• Apply changes to JcaPublicKeyDataDecryptorFactory
• Implement JcaExternalPublicKeyDataDecryptorFactory
• Consider reworking YubikeyPublicKeyDataDecryptorFactory to implement both a BC and JCA version.

[ligefeiBouncycastle]

Hi @vanitasvitae,
Thanks for the JCE work, it closes all three TODOs from the PR description, and I see you landed on the same conclusion we did about moving PublicKeyCryptoCallback out of AbstractPublicKeyDataDecryptorFactory.

Before going further, would you mind resyncing the branch onto current main and continuing from there? The earlier state of this PR is already merged, with a review pass on top, so working from current main means you can see what we've changed, and your own commits won't be masked by the ~4000 commits of drift. It also makes anything you need from our side easy to pick up.

Worth rebasing rather than merging: a few of the files you touched were adjusted in that review pass, so a rebase will surface those as conflicts you can resolve deliberately, where a merge would quietly take the older versions.

One heads-up for when you do, there are some debug leftovers still on the branch: options.debug = true in build.gradle, a printStackTrace callback added to OpenPGPMessageProcessor, and System.out.println calls in the Bc/Jce YubiKey factories that hex-dump recovered session keys and shared secrets.

Thank you.

[vanitasvitae]

Hey! I rebased the PR and added some more tests and further progress. I like the changes you applied!
Though in the future I'd prefer to have git commit authorship preserved if possible :)

[dghgit]

Merged with some revisions - I moved the external public key code under a new package org.bouncycastle.openpgp.api.operator. have a feeling it may serve us well to preserve the bcpg->openpgp->openpgp.api pattern. One thing, with debug, you can now just use:

./gradlew -Prelease.debug=true clean build

to do a debug build without having to change the build.gradle file.

The new API is now available at https://www.bouncycastle.org/betas as well