Convert cloud_fraction/cldfrc to CCPP and move to atmospheric_physics

[jimmielin]

What is the feature/what would you like to discuss?

Part of #1225

This is the accompanying issue for the first-stage cleanup PR for CCPPizing rk_stratiform_tend (CAM4).

This will only affect CAM4 and CAM5 physics, which use cloud_fraction.

Is there anyone in particular you want to be part of this conversation?

No response

Will this change (regression test) answers?

Yes

Will you be implementing this enhancement yourself?

Yes