gh-106320: Remove private _PyUnicode C API (#107185)

Move private _PyUnicode functions to the internal C API
(pycore_unicodeobject.h):

* _PyUnicode_IsCaseIgnorable()
* _PyUnicode_IsCased()
* _PyUnicode_IsXidContinue()
* _PyUnicode_IsXidStart()
* _PyUnicode_ToFoldedFull()
* _PyUnicode_ToLowerFull()
* _PyUnicode_ToTitleFull()
* _PyUnicode_ToUpperFull()

No longer export these functions.

Author: vstinner

Include/cpython/unicodeobject.h

@@ -473,14 +473,6 @@ PyAPI_FUNC(int) _PyUnicode_IsTitlecase(
     Py_UCS4 ch       /* Unicode character */
     );
 
-PyAPI_FUNC(int) _PyUnicode_IsXidStart(
-    Py_UCS4 ch       /* Unicode character */
-    );
-
-PyAPI_FUNC(int) _PyUnicode_IsXidContinue(
-    Py_UCS4 ch       /* Unicode character */
-    );
-
 PyAPI_FUNC(int) _PyUnicode_IsWhitespace(
     const Py_UCS4 ch         /* Unicode character */
     );
@@ -501,34 +493,6 @@ PyAPI_FUNC(Py_UCS4) _PyUnicode_ToTitlecase(
     Py_UCS4 ch       /* Unicode character */
     );
 
-PyAPI_FUNC(int) _PyUnicode_ToLowerFull(
-    Py_UCS4 ch,       /* Unicode character */
-    Py_UCS4 *res
-    );
-
-PyAPI_FUNC(int) _PyUnicode_ToTitleFull(
-    Py_UCS4 ch,       /* Unicode character */
-    Py_UCS4 *res
-    );
-
-PyAPI_FUNC(int) _PyUnicode_ToUpperFull(
-    Py_UCS4 ch,       /* Unicode character */
-    Py_UCS4 *res
-    );
-
-PyAPI_FUNC(int) _PyUnicode_ToFoldedFull(
-    Py_UCS4 ch,       /* Unicode character */
-    Py_UCS4 *res
-    );
-
-PyAPI_FUNC(int) _PyUnicode_IsCaseIgnorable(
-    Py_UCS4 ch         /* Unicode character */
-    );
-
-PyAPI_FUNC(int) _PyUnicode_IsCased(
-    Py_UCS4 ch         /* Unicode character */
-    );
-
 PyAPI_FUNC(int) _PyUnicode_ToDecimalDigit(
     Py_UCS4 ch       /* Unicode character */
     );

Include/internal/pycore_unicodeobject.h

@@ -11,6 +11,19 @@ extern "C" {
 #include "pycore_fileutils.h"     // _Py_error_handler
 #include "pycore_ucnhash.h"       // _PyUnicode_Name_CAPI
 
+/* --- Characters Type APIs ----------------------------------------------- */
+
+extern int _PyUnicode_IsXidStart(Py_UCS4 ch);
+extern int _PyUnicode_IsXidContinue(Py_UCS4 ch);
+extern int _PyUnicode_ToLowerFull(Py_UCS4 ch, Py_UCS4 *res);
+extern int _PyUnicode_ToTitleFull(Py_UCS4 ch, Py_UCS4 *res);
+extern int _PyUnicode_ToUpperFull(Py_UCS4 ch, Py_UCS4 *res);
+extern int _PyUnicode_ToFoldedFull(Py_UCS4 ch, Py_UCS4 *res);
+extern int _PyUnicode_IsCaseIgnorable(Py_UCS4 ch);
+extern int _PyUnicode_IsCased(Py_UCS4 ch);
+
+/* --- Unicode API -------------------------------------------------------- */
+
 PyAPI_FUNC(int) _PyUnicode_CheckConsistency(
     PyObject *op,
     int check_content);