Constrainable#getDeclaringClass() somehow breaks the new reflection abstraction
Let's see if we can improve it or if we keep it that way.
There are 2 issues here:
Callable is highly dependent to getDeclaringClass(). Not sure how to deal with it: whether we should have a lot of methods in Callable to try to solve the issue or consider Callable as a JavaBean only thing.
Let's say we move getDeclaringClass() from Constrainable to Callable: we still have a few issues to solve: we need an identifier for the declaring element: this is easily solvable. But we also have a big issue in ValidatorImpl: