RFR: JDK-8202016: Use obj+offset in interpreter array access

[Roman Kennke]

In the TemplateTable::aastore() and
InterpreterMacroAssembler::load_resolved_reference_at_index(), the
element address is flattened, and then passed to the BarrierSetAssembler
for actual access. GCs like Shenandoah need the original obj though.

The proposed change replaces the flattening with base+index+disp
addressing, and removes the shift and add computations. In the case of
aastore, we need to re-fetch the rcx/index from the stack because it
gets trashed on the way.

Testing: passed: hotspot/jtreg:tier1

Can I please get a review?
Thanks, Roman