cpp: Factor out common code of GpgME::engineInfo() overloads
* lang/cpp/src/context.cpp (get_engine_info, get_static_engine_info): New. (GpgME::engineInfo(GpgME::Protocol), GpgME::engineInfo(GpgME::Engine)): Use get_static_engine_info().
- GnuPG-bug-id: T5722