gh-110964: Remove private _PyArg functions (#110966)

Move the following private functions and structures to
pycore_modsupport.h internal C API:

* _PyArg_BadArgument()
* _PyArg_CheckPositional()
* _PyArg_NoKeywords()
* _PyArg_NoPositional()
* _PyArg_ParseStack()
* _PyArg_ParseStackAndKeywords()
* _PyArg_Parser structure
* _PyArg_UnpackKeywords()
* _PyArg_UnpackKeywordsWithVararg()
* _PyArg_UnpackStack()
* _Py_ANY_VARARGS()

Changes:

* Python/getargs.h now includes pycore_modsupport.h to export
  functions.
* clinic.py now adds pycore_modsupport.h when one of these functions
  is used.
* Add pycore_modsupport.h includes when a C extension uses one of
  these functions.
* Define Py_BUILD_CORE_MODULE in C extensions which now include
  directly or indirectly (via code generated by Argument Clinic)
  pycore_modsupport.h:

  * _csv
  * _curses_panel
  * _dbm
  * _gdbm
  * _multiprocessing.posixshmem
  * _sqlite.row
  * _statistics
  * grp
  * resource
  * syslog

* _testcapi: bad_get() no longer uses METH_FASTCALL calling
  convention but METH_VARARGS. Replace _PyArg_UnpackStack() with
  PyArg_ParseTuple().
* _testcapi: add PYTESTCAPI_NEED_INTERNAL_API macro which is defined
  by _testcapi sub-modules which need the internal C API
  (pycore_modsupport.h): exceptions.c, float.c, vectorcall.c,
  watchers.c.
* Remove Include/cpython/modsupport.h header file.
  Include/modsupport.h no longer includes the removed header file.
* Fix mypy clinic.py

PC/_wmimodule.cpp

@@ -8,6 +8,11 @@
 // Version history
 //  2022-08: Initial contribution (Steve Dower)
 
+// clinic/_wmimodule.cpp.h uses internal pycore_modsupport.h API
+#ifndef Py_BUILD_CORE_BUILTIN
+#  define Py_BUILD_CORE_MODULE 1
+#endif
+
 #define _WIN32_DCOM
 #include <Windows.h>
 #include <comdef.h>

PC/clinic/_testconsole.c.h

@@ -6,6 +6,7 @@ preserve
 #  include "pycore_gc.h"          // PyGC_Head
 #  include "pycore_runtime.h"     // _Py_ID()
 #endif
+#include "pycore_modsupport.h"    // _PyArg_UnpackKeywords()
 
 #if defined(MS_WINDOWS)
 
@@ -139,4 +140,4 @@ exit:
 #ifndef _TESTCONSOLE_READ_OUTPUT_METHODDEF
     #define _TESTCONSOLE_READ_OUTPUT_METHODDEF
 #endif /* !defined(_TESTCONSOLE_READ_OUTPUT_METHODDEF) */
-/*[clinic end generated code: output=f59fe72cd4e73704 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=08a1c844b3657272 input=a9049054013a1b77]*/

PC/clinic/_wmimodule.cpp.h

@@ -6,6 +6,7 @@ preserve
 #  include "pycore_gc.h"          // PyGC_Head
 #  include "pycore_runtime.h"     // _Py_ID()
 #endif
+#include "pycore_modsupport.h"    // _PyArg_UnpackKeywords()
 
 PyDoc_STRVAR(_wmi_exec_query__doc__,
 "exec_query($module, /, query)\n"
@@ -68,4 +69,4 @@ _wmi_exec_query(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObj
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=53821e597fc2aca4 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=ba04920d127f3ceb input=a9049054013a1b77]*/

PC/clinic/msvcrtmodule.c.h

@@ -2,6 +2,8 @@
 preserve
 [clinic start generated code]*/
 
+#include "pycore_modsupport.h"    // _PyArg_CheckPositional()
+
 PyDoc_STRVAR(msvcrt_heapmin__doc__,
 "heapmin($module, /)\n"
 "--\n"
@@ -695,4 +697,4 @@ exit:
 #ifndef MSVCRT_GETERRORMODE_METHODDEF
     #define MSVCRT_GETERRORMODE_METHODDEF
 #endif /* !defined(MSVCRT_GETERRORMODE_METHODDEF) */
-/*[clinic end generated code: output=525ec6ac4e3cb4f2 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=de9687b46212c2ed input=a9049054013a1b77]*/

PC/clinic/winreg.c.h

@@ -7,6 +7,7 @@ preserve
 #  include "pycore_runtime.h"     // _Py_ID()
 #endif
 #include "pycore_long.h"          // _PyLong_UnsignedLong_Converter()
+#include "pycore_modsupport.h"    // _PyArg_CheckPositional()
 
 #if (defined(MS_WINDOWS_DESKTOP) || defined(MS_WINDOWS_SYSTEM) || defined(MS_WINDOWS_GAMES))
 
@@ -1761,4 +1762,4 @@ exit:
 #ifndef WINREG_QUERYREFLECTIONKEY_METHODDEF
     #define WINREG_QUERYREFLECTIONKEY_METHODDEF
 #endif /* !defined(WINREG_QUERYREFLECTIONKEY_METHODDEF) */
-/*[clinic end generated code: output=d7ae41899af53d7c input=a9049054013a1b77]*/
+/*[clinic end generated code: output=1ee4098b2f143b6a input=a9049054013a1b77]*/

PC/clinic/winsound.c.h

@@ -6,6 +6,7 @@ preserve
 #  include "pycore_gc.h"          // PyGC_Head
 #  include "pycore_runtime.h"     // _Py_ID()
 #endif
+#include "pycore_modsupport.h"    // _PyArg_UnpackKeywords()
 
 PyDoc_STRVAR(winsound_PlaySound__doc__,
 "PlaySound($module, /, sound, flags)\n"
@@ -205,4 +206,4 @@ skip_optional_pos:
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=21584101f656198f input=a9049054013a1b77]*/
+/*[clinic end generated code: output=191d4fb1542c7abf input=a9049054013a1b77]*/

PC/winsound.c

@@ -35,6 +35,11 @@
    winsound.PlaySound(None, 0)
 */
 
+// clinic/winsound.c.h uses internal pycore_modsupport.h API
+#ifndef Py_BUILD_CORE_BUILTIN
+#  define Py_BUILD_CORE_MODULE 1
+#endif
+
 #include <Python.h>
 #include <windows.h>
 #include <mmsystem.h>