Issue #11223: Add threading._info() function providing informations about the

Issue #11223: Add threading._info() function providing informations about the
thread implementation.

Skip test_lock_acquire_interruption() and test_rlock_acquire_interruption() of
test_threadsignals if a thread lock is implemented using a POSIX mutex and a
POSIX condition variable. A POSIX condition variable cannot be interrupted by a
signal (e.g. on Linux, the futex system call is restarted).