gh-93937, C API: Move PyFrame_GetBack() to Python.h (#93938)

Move the follow functions and type from frameobject.h to pyframe.h,
so the standard <Python.h> provide frame getter functions:

* PyFrame_Check()
* PyFrame_GetBack()
* PyFrame_GetBuiltins()
* PyFrame_GetGenerator()
* PyFrame_GetGlobals()
* PyFrame_GetLasti()
* PyFrame_GetLocals()
* PyFrame_Type

Remove #include "frameobject.h" from many C files. It's no longer
needed.