Avoid loading Klass* twice in TypeArrayKlass::oop_size()

TypeArrayKlass::oop_size() calls into TypeArrayOopDesc::object_size() which loads the Klass* from the object, but this is not necessary because we're coming from TypeArrayKlass.

Note: This came up in Lilliput, where we need to be careful how to load the Klass, and must figure out the object size using oopDesc::size_given_klass() without blindly re-loading the Klass*.