feat: better private properties handling

[nikophil]

What this PR does:

• fixes the case where source object have private parameters in their constructor
• add a way to call private mutators with extractCallbacks, the same way it's already done for private property access
• add a parameter mapPrivateProperties and use it to decide whether to force private properties/mutators

fixes #2

[Korbeil]

Thanks for your contribution @nikophil ! 🙏