ipa-kdb: refactor MS-PAC processing to prepare for krb5 1.20
    
    Make sure both krb5 pre 1.20 and 1.20 or later would call into the same
    PAC generation code while driven by different API callbacks from the
    krb5 KDB interface.
    
    Fixes: https://pagure.io/freeipa/issue/9083
    Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Julien Rische <jrische@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Julien Rische <jrische@redhat.com>