Sequoia should be able to distinguish first-party-attested third-party certifications (1pa3pc)

First-party attestations of third-party certifications are a way that a keystore can demonstrate sovereignty over a TPK ("OpenPGP certificate").

It would be great if Sequoia could expose an interface that makes it easy to tell which certifications are attested to by the primary key of the certificate.

Here is an example that shows an attested third-party certification:

This is the third-party:

-----BEGIN PGP PUBLIC KEY BLOCK-----

xjMEXWxT2xYJKwYBBAHaRw8BAQdAlkEdNNqQkawuTGUH1GrfLUqHDrbUaE01xgm0
oOD5xSLNJkNlcnRpZmljYXRlIEF1dGhvcml0eSA8Y2FAZXhhbXBsZS5jb20+wm0E
ExYIABUFAl1sU9sCGwECFQgCF4ACGQECHgEACgkQOZoABDr0aMje2QD/Q8LsqS6L
9DsRTSERK1HGN14s7Uiw3GmjJCewLGCrFTcBAOmkKq7l5ZWrS+5E0sj8q+nSsqDG
f44T9U4D9WccPAgI
=deVv
-----END PGP PUBLIC KEY BLOCK-----

This is the certificate that contains a self-sig, a third-party certification, and an attestation from the first party over the third-party certification:

-----BEGIN PGP PUBLIC KEY BLOCK-----
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=PUbv
-----END PGP PUBLIC KEY BLOCK-----