feat: StoppableEventInterface implementation

Since v3 still targets PHP versions prior to PHP 7.2, this patch
provides a forwards-compatibility shim for the PSR-14
`StoppableEventInterface` via an additional, package-specific version
that is now also implemented by default in the `Event` class.

Author: weierophinney

src/Event.php

@@ -1,10 +1,8 @@
 <?php
 /**
- * Zend Framework (http://framework.zend.com/)
- *
- * @link      http://github.com/zendframework/zend-eventmanager for the canonical source repository
- * @copyright Copyright (c) 2005-2015 Zend Technologies USA Inc. (http://www.zend.com)
- * @license   https://github.com/zendframework/zend-eventmanager/blob/master/LICENSE.md
+ * @see       https://github.com/zendframework/zend-eventmanager for the canonical source repository
+ * @copyright Copyright (c) 2005-2019 Zend Technologies USA Inc. (https://www.zend.com)
+ * @license   https://github.com/zendframework/zend-eventmanager/blob/master/LICENSE.md New BSD License
  */
 
 namespace Zend\EventManager;
@@ -17,7 +15,7 @@
  * Encapsulates the target context and parameters passed, and provides some
  * behavior for interacting with the event manager.
  */
-class Event implements EventInterface
+class Event implements EventInterface, StoppableEventInterface
 {
     /**
      * @var string Event name
@@ -192,10 +190,20 @@ public function stopPropagation($flag = true)
     /**
      * Is propagation stopped?
      *
+     * @deprecated Use isPropagationStopped instead, to make your application
+     *     forwards-compatible with PSR-14 and zend-eventmanager v4.
      * @return bool
      */
     public function propagationIsStopped()
     {
         return $this->stopPropagation;
     }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function isPropagationStopped()
+    {
+        return $this->stopPropagation;
+    }
 }

src/EventInterface.php

@@ -90,6 +90,8 @@ public function stopPropagation($flag = true);
     /**
      * Has this event indicated event propagation should stop?
      *
+     * @deprecated Implement StoppableEventInterface instead, to make your
+     *     application forwards-compatible with PSR-14 and zend-eventmanager v4.
      * @return bool
      */
     public function propagationIsStopped();

src/StoppableEventInterface.php

@@ -0,0 +1,22 @@
+<?php
+/**
+ * @see       https://github.com/zendframework/zend-eventmanager for the canonical source repository
+ * @copyright Copyright (c) 2019 Zend Technologies USA Inc. (https://www.zend.com)
+ * @license   https://github.com/zendframework/zend-eventmanager/blob/master/LICENSE.md New BSD License
+ */
+
+namespace Zend\EventManager;
+
+/**
+ * Forwards-compatibility shim for the PSR-14 StoppableEventInterface
+ *
+ * This interface can be mixed into the `Event` instance to make it
+ * forwards-compatible with PSR-14.
+ */
+interface StoppableEventInterface
+{
+    /**
+     * @return bool
+     */
+    public function isPropagationStopped();
+}