2.16.0 removes FormElementManager::get()

[rieschl]

BC Break Report

Q	A
Version	2.16.0

Summary

When refactoring the FormElementManager class in #75 and removing support for service-manager v2 the V3Polyfill and FormElementManagerTrait were copied together to a "real" FormElementManager class.
But it seems that the previous method \Laminas\Form\FormElementManager\FormElementManagerTrait::get wasn't copied.
The main purpose of that method was calling \Laminas\Form\FormElementManager::setInvokableClass() for invokable Forms to override the default InovkableFactory with \Laminas\Form\ElementFactory.

Previous behavior

Invokable Forms (and probably all other Elements and Fieldsets) were created with the \Laminas\Form\ElementFactory.

Current behavior

Invokable Forms with options are instantiated incorrectly, because \Laminas\ServiceManager\Factory\InvokableFactory instantiates the object differently.

How to reproduce

Fetch a Form with options from the FormElementManager

$this->formElementManager->get(Form::class, ['foo' => 'bar']);

Previously, when no custom factory was registered, FormElementManagerTrait::get called FormElementManager::setInvokableClass to use ElementFactory, which creates the object with return new $requestedName($name, $options);. Now, this is missing, causing InvokableFactory to instantiate the class with new $requestedName($options), using the options array as form name.
The default constructor for Fieldset which Form extends from, is public function __construct($name = null, $options = []).
The options array is used as form name and later on, when rendering the form, the escaper view helper throws up when trying to escape the name atrribute of the form opening tag because it's an array and not a string.

[Slamdunk]

Fixed by #93