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

Python/clinic/Python-tokenize.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()
 
 static PyObject *
 tokenizeriter_new_impl(PyTypeObject *type, PyObject *readline,
@@ -79,4 +80,4 @@ skip_optional_kwonly:
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=406b5a433a59069c input=a9049054013a1b77]*/
+/*[clinic end generated code: output=dcd6ec48f06a092e input=a9049054013a1b77]*/

Python/clinic/_warnings.c.h

@@ -7,6 +7,7 @@ preserve
 #  include "pycore_runtime.h"     // _Py_ID()
 #endif
 #include "pycore_abstract.h"      // _PyNumber_Index()
+#include "pycore_modsupport.h"    // _PyArg_UnpackKeywords()
 
 PyDoc_STRVAR(warnings_warn__doc__,
 "warn($module, /, message, category=None, stacklevel=1, source=None, *,\n"
@@ -243,4 +244,4 @@ warnings_filters_mutated(PyObject *module, PyObject *Py_UNUSED(ignored))
 {
     return warnings_filters_mutated_impl(module);
 }
-/*[clinic end generated code: output=8c396a721ef75739 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=f2d4214c382717a6 input=a9049054013a1b77]*/

Python/clinic/bltinmodule.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(builtin___import____doc__,
 "__import__($module, /, name, globals=None, locals=None, fromlist=(),\n"
@@ -1211,4 +1212,4 @@ builtin_issubclass(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=607c62f2341ebfc0 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=31bded5d08647a57 input=a9049054013a1b77]*/

Python/clinic/context.c.h

@@ -2,6 +2,8 @@
 preserve
 [clinic start generated code]*/
 
+#include "pycore_modsupport.h"    // _PyArg_CheckPositional()
+
 PyDoc_STRVAR(_contextvars_Context_get__doc__,
 "get($self, key, default=None, /)\n"
 "--\n"
@@ -177,4 +179,4 @@ PyDoc_STRVAR(_contextvars_ContextVar_reset__doc__,
 
 #define _CONTEXTVARS_CONTEXTVAR_RESET_METHODDEF    \
     {"reset", (PyCFunction)_contextvars_ContextVar_reset, METH_O, _contextvars_ContextVar_reset__doc__},
-/*[clinic end generated code: output=2436b16a92452869 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=b667826178444c3f input=a9049054013a1b77]*/

Python/clinic/import.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_CheckPositional()
 
 PyDoc_STRVAR(_imp_lock_held__doc__,
 "lock_held($module, /)\n"
@@ -626,4 +627,4 @@ exit:
 #ifndef _IMP_EXEC_DYNAMIC_METHODDEF
     #define _IMP_EXEC_DYNAMIC_METHODDEF
 #endif /* !defined(_IMP_EXEC_DYNAMIC_METHODDEF) */
-/*[clinic end generated code: output=058f6aa1c9f4ebe4 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=c37ad1bf06f9e947 input=a9049054013a1b77]*/

Python/clinic/instrumentation.c.h

@@ -2,6 +2,8 @@
 preserve
 [clinic start generated code]*/
 
+#include "pycore_modsupport.h"    // _PyArg_CheckPositional()
+
 PyDoc_STRVAR(monitoring_use_tool_id__doc__,
 "use_tool_id($module, tool_id, name, /)\n"
 "--\n"
@@ -302,4 +304,4 @@ monitoring__all_events(PyObject *module, PyObject *Py_UNUSED(ignored))
 {
     return monitoring__all_events_impl(module);
 }
-/*[clinic end generated code: output=46f449b18195f976 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=14ffc0884a6de50a input=a9049054013a1b77]*/

Python/clinic/marshal.c.h

@@ -2,6 +2,8 @@
 preserve
 [clinic start generated code]*/
 
+#include "pycore_modsupport.h"    // _PyArg_CheckPositional()
+
 PyDoc_STRVAR(marshal_dump__doc__,
 "dump($module, value, file, version=version, /)\n"
 "--\n"
@@ -155,4 +157,4 @@ exit:
 
     return return_value;
 }
-/*[clinic end generated code: output=23091e077319f596 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=99ba446b1a75a269 input=a9049054013a1b77]*/

Python/clinic/sysmodule.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(sys_addaudithook__doc__,
 "addaudithook($module, /, hook)\n"
@@ -1451,4 +1452,4 @@ exit:
 #ifndef SYS_GETANDROIDAPILEVEL_METHODDEF
     #define SYS_GETANDROIDAPILEVEL_METHODDEF
 #endif /* !defined(SYS_GETANDROIDAPILEVEL_METHODDEF) */
-/*[clinic end generated code: output=3a7d3fbbcb281c22 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=f36d45c829250775 input=a9049054013a1b77]*/

Python/clinic/traceback.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(tb_new__doc__,
 "TracebackType(tb_next, tb_frame, tb_lasti, tb_lineno)\n"
@@ -77,4 +78,4 @@ tb_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=57e27eb68d04d842 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=4e2f6b935841b09c input=a9049054013a1b77]*/

Python/getargs.c

@@ -4,6 +4,7 @@
 #include "Python.h"
 #include "pycore_abstract.h"      // _PyNumber_Index()
 #include "pycore_dict.h"          // _PyDict_HasOnlyStringKeys()
+#include "pycore_modsupport.h"    // export _PyArg_NoKeywords()
 #include "pycore_pylifecycle.h"   // _PyArg_Fini
 #include "pycore_tuple.h"         // _PyTuple_ITEMS()