bpo-32096: Remove obj and mem from _PyRuntime (#4532)

bpo-32096, bpo-30860:  Partially revert the commit
2ebc5ce42a8a9e047e790aefbf9a94811569b2b6:

* Move structures back from Include/internal/mem.h to
  Objects/obmalloc.c
* Remove _PyObject_Initialize() and _PyMem_Initialize()
* Remove Include/internal/pymalloc.h
* Add test_capi.test_pre_initialization_api():
   Make sure that it's possible to call Py_DecodeLocale(), and then call
   Py_SetProgramName() with the decoded string, before Py_Initialize().

PyMem_RawMalloc() and Py_DecodeLocale() can be called again before
_PyRuntimeState_Init().

Co-Authored-By: Eric Snow <ericsnowcurrently@gmail.com>