bpo-44113: Deprecate old functions to config Python init (GH-26060)

Deprecate the following functions to configure the Python
initialization:

* PySys_AddWarnOption()
* PySys_AddWarnOptionUnicode()
* PySys_AddXOption()
* PySys_HasWarnOptions()
* Py_SetPath()
* Py_SetProgramName()
* Py_SetPythonHome()
* Py_SetStandardStreamEncoding()
* _Py_SetProgramFullPath()

Use the new PyConfig API of the Python Initialization Configuration
instead (PEP 587).

Programs/_testembed.c

@@ -22,6 +22,11 @@
 /* Use path starting with "./" avoids a search along the PATH */
 #define PROGRAM_NAME L"./_testembed"
 
+// Ignore Py_DEPRECATED() compiler warnings: deprecated functions are
+// tested on purpose here.
+_Py_COMP_DIAG_PUSH
+_Py_COMP_DIAG_IGNORE_DEPR_DECLS
+
 static void _testembed_Py_Initialize(void)
 {
     Py_SetProgramName(PROGRAM_NAME);