gh-115942: Add locked to several multiprocessing locks (#115944)

Co-authored-by: mpage <mpage@cs.stanford.edu>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

Lib/multiprocessing/synchronize.py

@@ -90,6 +90,9 @@ class SemLock(object):
         self.acquire = self._semlock.acquire
         self.release = self._semlock.release
 
+    def locked(self):
+        return self._semlock._count() != 0
+
     def __enter__(self):
         return self._semlock.__enter__()