Add missing annotation to mutex_lock's move constructor.

Because ~mutex_lock() is marked as an UNLOCK_FUNCTION, we have to mark
the move constructor as locking ml.mu_.  Otherwise if you try to move a
mutex_lock, clang sees the destructor call and thinks that the mutex has
been unlocked for good.

Same for tf_shared_lock.

Also make tf_shared_lock's move constructor non-explicit.  This is just
a performance optimization; tf_shared_lock was already copyable.

PiperOrigin-RevId: 207610922