8367989: Remove InstanceKlass::allocate_objArray

[coleenp]

This change removes InstanceKlass::allocate_objArray and has its caller call ObjArrayKlass::allocate_instance directly from oopFactory, like the other array allocations do. See CR for more information why we should have this change. I also removed element_klass_addr() and moved element_klass_offset() to be in a more logical place near element_klass() functions. This upstreams a tiny valhalla diff.
Tested with tier1-4.

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• JDK-8367989: Remove InstanceKlass::allocate_objArray (Enhancement - P4)

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