Add support for callbacks in deserialization lifecycle

[noemi-salaun]

We should add support for deserlization callbacks, something like

interface Deserializable {
   beforeDeserialize(event);
   afterDeserialize(event);
}

class Foo implements Deserializable {
   attr1: string;

   @DeserializeAs(Bar)
   attr2: Bar;

   beforeDeserialize(event) {
       event.json.attr1 = event.json.attr1 + '-modified';
   }

   afterDeserialize(event) {
      event.target.attr2.setSomething(event.json.something);
   }
}

We should also support function in place of class inside @DeserializeAs decorator.

const myFunc = (json) => {
    return json.someAttr + ' - ' + json.someOtherAttr;
}

class Foo {
    attr1: string;
 
    @DeserializeAs(myFunc)
    attr2: Bar;
}

All the proposed signature are fakes

[Supamiu]

We should define what has to be in event in this issue, then the implementation will be easy.