cpp: Add support for gpgme_op_setexpire
* lang/cpp/src/context.cpp (Context::setExpire, Context::startSetExpire): New. (Context::getLFSeparatedListOfFingerprintsFromSubkeys): New helper. * lang/cpp/src/context.h (Context::SetExpireFlags): New enum. (Context::setExpire, Context::startSetExpire): Add prototypes. (Context::getLFSeparatedListOfFingerprintsFromSubkeys): Add as private helper.
- GnuPG-bug-id: T5003