minor #9765 Updated from new MyFormType() to MyFormType::class (ThomasLandauer)

This PR was submitted for the 2.7 branch but it was merged into the 2.8 branch instead (closes #9765).

Discussion
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Updated from `new MyFormType()` to `MyFormType::class`

Passing a new instance of the form type gave me this error:

> Type error: Argument 1 passed to Symfony\Component\Form\Extension\Core\EventListener\ResizeFormListener::__construct() must be of the type string, object given

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Commits
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b031b97 Updated from `new MyFormType()` to `MyFormType::class`

Author: xabbuh

reference/forms/types/collection.rst

@@ -340,8 +340,8 @@ entry_type
 This is the field type for each item in this collection (e.g. ``TextType``,
 ``ChoiceType``, etc). For example, if you have an array of email addresses,
 you'd use the :doc:`EmailType </reference/forms/types/email>`. If you want
-to embed a collection of some other form, create a new instance of your
-form type and pass it as this option.
+to embed a collection of some other form, pass the form type class as this
+option (e.g. ``MyFormType::class``)
 
 prototype
 ~~~~~~~~~