Upstream Array rework from Valhalla repository

[coleenp]

This change upstreams some changes in the Valhalla repo that refactored arrays into ObjArrayKlass - that holds the Java type links (points back and forth to mirror) and RefArrayKlass which are the metadata that represents the physical layout of Java array objects in the heap. RefArrayKlass._super points to ObjArrayKlass (the java Type) so that checkcast works (except in c2 in this patch because it's broken).

There's still a significant amount of compiler work that needs to be done for this change. https://bugs.openjdk.org/browse/JDK-8366668

Not really tested. Just builds with c1.

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[liach]

Should core libs port the part where array base offset/index scale etc. are now per-instance?

[coleenp]

Should core libs port the part where array base offset/index scale etc. are now per-instance?

With this patch refArrayKlass and objArrayKlass have the same array base offset and index scale, so I don't know this yet.