[3.12] gh-109047: concurrent.futures catches RuntimeError (#109810)

[vstinner]

concurrent.futures: The executor manager thread now catches exceptions when adding an item to the call queue. During Python finalization, creating a new thread can now raise RuntimeError. Catch the exception and call terminate_broken() in this case.

Add test_python_finalization_error() to test_concurrent_futures.

concurrent.futures._ExecutorManagerThread changes:

• terminate_broken() no longer calls shutdown_workers() since the call queue is no longer working anymore (read and write ends of the queue pipe are closed).
• terminate_broken() now terminates child processes, not only wait until they complete.
• _ExecutorManagerThread.terminate_broken() now holds shutdown_lock to prevent race conditons with ProcessPoolExecutor.submit().

multiprocessing.Queue changes:

• Add _terminate_broken() method.
• _start_thread() sets _thread to None on exception to prevent leaking "dangling threads" even if the thread was not started yet.

(cherry picked from commit 6351842)

• Issue: test_concurrent_futures.test_shutdown: test_interpreter_shutdown() fails randomly (race condition) #109047