Add missing type hint and correct deprecation text.

Summary of Changes

The $state property defined in the StateBehaviorTrait has as type hint the State class which is deprecated. The goal is to replace the State object with a Registry object. This can be done in 5.0+ by initialising the $state in the constructor with a Registry object. The Trait will use this Registry object. If the $state property is not type hinted with the Registry object, phpstan will complain about incorrect use of the $state.

This PR allows to use the correct type (Registry) and solves warnings from the static code analyser.

Testing Instructions

Code Review.

if you use phpstan you should no longer get the following messages:

Initialization of $state with \Joomla\Registry\Registry in the constructor

class YourModel extends ListModel
{
    public function __construct($config = [], ?MVCFactoryInterface $factory = null)
    {
        $this->state = new Registry();
    }
}

Property Joomla\CMS\MVC\Model\BaseModel::$state (Joomla\CMS\MVC\Model\State) does not accept Joomla\Registry\Registry.  
         🪪  assign.propertyType                                                                                                 

Get variable from the $state property when it's a State object

class YourModel extends ListModel
{
    public function getItems()
    {
        return $this->state->get('dummy);
    }
    public function getItems2()
    {
        return $this->getState('dummy);
    }
}

Call to method get() of deprecated class Joomla\CMS\MVC\Model\State:                                                    
         7.0 Use the Registry directly                                                                                           
         🪪  method.deprecatedClass                                                                                              

Also if you run this code against the State object you get a runtime E_USER_DEPRECATED warning.

Actual result BEFORE applying this Pull Request

With phpstan warnings and E_USER_DEPRECATED for the get function is triggered.

Expected result AFTER applying this Pull Request

Without phpstan warnings and no E_USER_DEPRECATED for the get function is triggered.

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed