Provide instance reference for constructor calls.

[safesparrow]

Description

instance parameter in the IMethodDecorator.Init method is currently null for constructor calls.
As described in #71 , it can be useful to have a reference to the instance.

The solution

The PR provides the instance reference for constructors. Now the only time the reference is not provided is for static members.

One caveat with this is that the object is only fully initialized after the constructor has finished, so providing the reference could cause issues if it's used for operations that require a fully initialized object.

Maybe this should be configurable by the user and disabled by default?

Todos

• Decide whether the solution is safe.
• Backwards-compatibility?
• Related issues - Constructor support of instance reference #71
• Fix existing tests
• Tests
• Documentation