[5.4] Return the used traits from setUpTraits

[Lidbetter]

Allows for the developer to add their own traits and actions during the setup phase without having to call: $uses = array_flip(class_uses_recursive(static::class)); in the subclass.

Example usage before:

    protected function setUpTraits()
    {
        parent::setUpTraits();
        $uses = array_flip(class_uses_recursive(static::class));

        if(isset($uses[MyGreatTrait::class])) {
            $this->runMyUsefulThing();
        }
    }

Example usage with change from this pr:

    protected function setUpTraits()
    {
        $uses = parent::setUpTraits();

        if(isset($uses[MyGreatTrait::class])) {
            $this->runMyUsefulThing();
        }

        return $uses;
    }

[mfn]

Great @Lidbetter just want I was thinking about the other day, thx!