Make setters return `this` to allow for fluent interfaces

[greg-at-moderne]

What problem are you trying to solve?

Nicer APIs.

Describe the situation before applying the recipe

public class Person {
    private int age;

    public void setAge(int age) {
        this.age = age;
    }
}

Describe the situation after applying the recipe

public class Person {
    private int age;

    public Person setAge(int age) {
       this.age = age;
       return this; // <--------------
    }
}

Any additional context

• One could consider doing the same to other methods returning void, not only the setters.
• I haven't thought it through though, maybe some heuristics is needed to pick which methods it would be relevant for.

[e5LA]

• Proposed implementation in Add FluentSetterRecipe #646