This PR improves some scenarios regarding instance variables initializers.
The solution is a workaround that collect & expand later the initializers.

A better long term solution would be to decouple analyze ivar initializers and the instantiation of #initialize methods. Like adding a phase that will remove syntactic ivar initializers in the class lexical scope and expand them in the initialize body, before the codegen. Hence in the codegen or further phases there is no need to track the concept of ivar initializers since they could be just a syntax sugar. NB: currently (before PR) ivar initializers are used in #allocate as well.

Fixes #3988