Remove some pieces from forcerec.h

Remove some pieces from forcerec.h

This makes it less of a global compilation dependency. Some new
includes required because contents were no longer available via
transitive inclusion. Used more forward declarations to avoid
such transitive inclusion.

Removed some C++ guards too now that some more pieces are no longer
compiled by most/all of the group scheme kernels.

Change-Id: I56a1bb290da639500dbc8c8baa04c1f32758713c