Adapt CFG translation for NewClassTree

[d367wang]

A new class tree is translated to the CFG node sequence as "type identifier -> anony class declaration -> anony constructor invocation".
Based on the sequence above, when dataflow analysis is running, visitIdentifier is run first, then visitClass, then visitNewClass. This causes crosscutting since all of these three spots have to check and handle anonymous classes as a special case (e.g. create extra slots and constraints), as shown in #325.

One solution to solve this issue is to adapt the CFG translation by representing NewClassTree with a single ObjectCreation node.