Split load fields through nested phi nodes

[dhanalla]

This change is to Reduce Phi that has a child Phi as user and the child is only used for field loads.

Here are the sequence of Ideal graph transformations for Nested phi optimizations:

1. Identify Nestedphi as potential candidate for optimization in ConnectionGraph::can_reduce_check_users
   ParentPhi->idx = 230
   Nestedphi->idx = 327

2. Split through nestedphi node (Nestedphi->idx = 327) before parent phi node (ParentPhi->idx = 230) in ConnectionGraph::reduce_phi

3. Split through parentphi node (ParentPhi->idx = 230) in ConnectionGraph::reduce_phi

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