WIP:p: NULL initialize dataAddr field for 0 size arrays

[VermaSh]

Update array inline allocation sequence to initialize dataAddr field
only for non-zero size arrays. Field should be left blank for zero
size arrays.

[VermaSh]

@zl-wang / @rmnattas here are my changes for inline allocation sequence on power. Marked it as WIP because I still need to investigate the failures.

[rmnattas]

I'm not sure if I'm understanding what's needed for this correctly but my understanding as bases of my following comments:
1- J9IndexableObjectDisontiguous is for arraylets mainly and not used for OffHeap, hence we only care about contiguous object shapes(?)
2- needZeroInit being false means that dataAddrField is assumed 0 already.

Listed the different cases the code handles to make sure each works correctly and comments are related to:
1- Places that use the disontiguous object shape dataAddrFieldOffset or headerSize which will be wrong in compressed ref (and confusing although correct in full ref)
2- Cases where needZeroInit is false but code writes obj+headerSize into dataAddrField even if array len is 0.

3 blocks
a) line 6519
b) line 6554
c) line 6564

8 cases
1) compressed & isVariableLen & needZeroInit
2) compressed & isVariableLen & !needZeroInit
3) compressed & !isVariableLen & needZeroInit
4) compressed & !isVariableLen & !needZeroInit
5) !compressed & isVariableLen & needZeroInit
6) !compressed & isVariableLen & !needZeroInit
7) !compressed & !isVariableLen & needZeroInit
8) !compressed & !isVariableLen & !needZeroInit


1,2 -> a: needZeroInit uses OffsetOfDiscontiguousDataAddrField? !needZeroInit uses OffsetOfContiguousDataAddrField correctly.
3 -> if-const-0 {b: use discontiguous offset?} else {c: uses contiguous offset}
4 -> c: needZeroInit is false but you always write to dataAddrField. If len is 0, you write obj+headerSize over the already 0 dataAddrField, right?
5,6 -> c: doesn't do the runtime check if len is 0, always set dataAddr = obj+headerSize
7 -> if-const-0 {b: use discontiguous offset?} else {c: uses contiguous offset}
8 -> c: doesn't do the runtime check if len is 0, always set dataAddr = obj+headerSize