Unify bytecode transformation logic for constructors (<init> methods) and regular methods.

[eupp]

Currently, the for <init> methods Lincheck applies different set of bytecode transformers, compared to regular methods. This often leads to bugs. We need to revisit this logic, and unify the logic of constructors and regular methods instrumentation.

However, note that for <init> methods we still need some additional checks to tackle "leaking this" problem, see #424