Clean up stopped test threads under ASAN

Summary:
AddressSanitizer can retain stopped TestThread objects after their OS threads have joined. This leaves those objects in threading._dangling and makes regrtest report ENV CHANGED even though all threading tests pass.

After joining every test thread and asserting that it has stopped, remove these test-owned objects from the private diagnostic weak set on ASAN builds. Normal builds retain the existing dangling-thread leak detection.

Keep the replayable 3.14 patch and its metadata synchronized with the patched tree.

Reviewed By: yoney

Differential Revision: D122693875

fbshipit-source-id: 9020eaac9da67d7625193dcde3f1feef81cff31e

Author: itamaro

Lib/test/test_threading.py

@@ -231,6 +231,9 @@ def test_various_ops(self):
         if verbose:
             print('all tasks done')
         self.assertEqual(numrunning.get(), 0)
+        if support.check_sanitizer(address=True):
+            # ASAN can retain stopped Thread objects after their OS threads join.
+            threading._dangling.difference_update(threads)
 
     def test_ident_of_no_threading_threads(self):
         # The ident still must work for the main thread and dummy threads.