On ResourceWarning, log traceback where the object was allocated

Issue #26567:

* Add a new function PyErr_ResourceWarning() function to pass the destroyed
  object
* Add a source attribute to warnings.WarningMessage
* Add warnings._showwarnmsg() which uses tracemalloc to get the traceback where
  source object was allocated.
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 77a6b31..657b04b 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -4170,8 +4170,7 @@
         Py_ssize_t old_refcount = Py_REFCNT(s);
         ++Py_REFCNT(s);
         PyErr_Fetch(&exc, &val, &tb);
-        if (PyErr_WarnFormat(PyExc_ResourceWarning, 1,
-                             "unclosed %R", s))
+        if (PyErr_ResourceWarning(s, 1, "unclosed %R", s))
             /* Spurious errors can appear at shutdown */
             if (PyErr_ExceptionMatches(PyExc_Warning))
                 PyErr_WriteUnraisable((PyObject *) s);