Fluent setters/functions

[jolelievre]

Add a rule for fluent setter, the rule is to be defined But I believe we expect the return type to be self instead of the class name

public function setValue($value): self
{
    $this->value = $value;

    return $this;
}

The idea is not to force all setters to be fluent, however when a function returns $this I guess we can consider it as a "fluent functions" so in this case we can expect its return type to be self