Remove TRAPS/THREAD parameter for class loading functions

find_constrained_instance_or_array_klass only passes THREAD so that it can be used in a MutexLocker for SystemDictionary_lock. This can use the MutexLocker that gets Thread::current() without any harm to performance.

The other functions add_loader_constraint, record_linking_constraints, and check_signature_loaders fall out from that.

check_signature_loaders should throw an exception but it unfortunately makes the caller construct the exception message so it doesn't.

Also: is_shared_class_visible{_impl}