Issue #28838: Rename parameters of the "calls" functions of the Python C API.

* Rename 'callable_object' and 'func' to 'callable': any Python callable object
  is accepted, not only Python functions
* Rename 'method' and 'nameid' to 'name' (method name)
* Rename 'o' to 'obj'
* Move, fix and update documentation of PyObject_CallXXX() functions
  in abstract.h
* Update also the documentaton of the C API (update parameter names)