Also updates TestFFDHE to exercise the new method (and, in doing so,
refactors the tests a bit).
The core check logic from exercise() is moved into a tryFFDHELookupByName
function, which is now used by both the exercise() test, as well as the
namedGroupsMethod() test that is added by this commit.
This commit adds a new class that gives access to the
Diffie-Hellman parameters from RFC 7919.
The class exposes a static function, PEMForNamedGroup, which
looks up a set of Diffie-Hellman parameters in PEM form by
the name used in RFC 7919.
For example, to get the PEM form of 'ffdhe2048', you would
call
QByteArray pem = FFDHE::PEMForNamedGroup(QLatin1String("ffdhe2048"));
With that in hand, you can pass the returned PEM data to
QSslDiffieHellmanParameters to construct an object that can be set
on a QSslSocket-based TLS server.
