Symfony FormTrait: should check instanceof instead of name

[caudurieau]

In the Symfony FormTrait instead of checking the classname to determinate if the class is a form, we should check if it implements the Symfony\Component\Form\FormTypeInterface.

Because there are no rules that impose to name forms with the word "Type" at the end of classnames. So you may name your forms for example with the word "Form" at the end of classnames.

Source:

• Forms best practices: https://symfony.com/doc/current/best_practices.html#forms
• Form creation: https://symfony.com/doc/current/forms.html