Re-export _Py_DumpTraceback and _Py_DumpTracebackThreads

These functions stopped being exported in #107215.  However, they are the only
way to print a Python stacktrace safely from a signal handler, making them very
useful for extensions.  Re-export them.

Author: alexmalyshev

Include/internal/pycore_traceback.h

@@ -31,7 +31,7 @@ PyAPI_FUNC(void) _PyTraceback_Add(const char *, const char *, int);
 
    This function is signal safe. */
 
-extern void _Py_DumpTraceback(
+PyAPI_FUNC(void) _Py_DumpTraceback(
     int fd,
     PyThreadState *tstate);
 
@@ -58,7 +58,7 @@ extern void _Py_DumpTraceback(
 
    This function is signal safe. */
 
-extern const char* _Py_DumpTracebackThreads(
+PyAPI_FUNC(const char*) _Py_DumpTracebackThreads(
     int fd,
     PyInterpreterState *interp,
     PyThreadState *current_tstate);