feat: Adds EventDispatchingInterface

Basically, a counterpart to the current EventManagerAwareInterface, but
for EventDispatcherInterface composition.

Also revises the Deprecations list, as we can keep EventManager as an
EventDispatcherInterface implementation for 4.0.

Author: weierophinney

TODO-PSR-14.md

@@ -88,15 +88,10 @@
     - [x] it will return the event itself
     - [x] it will need to validate that it received an object before calling
       `triggerListeners`
-- [ ] Additional utilities
-  - [ ] `EventDispatchingInterface` with a `getEventDispatcher()` method
-  - [ ] Alternate dispatcher implementation, `EventDispatcher`
-    - [ ] Should accept a listener provider interface to its constructor
-    - [ ] Should implement `EventDispatcherInterface` via duck-typing: it will
-        implement a `dispatch()` method only
+- [x] Additional utilities
+  - [x] `EventDispatchingInterface` with a `getEventDispatcher()` method
 - [ ] Deprecations
   - [ ] `EventInterface`
-  - [ ] `EventManager`
   - [ ] `EventManagerInterface`
   - [ ] `EventManagerAwareInterface`
   - [ ] `EventManagerAwareTrait`
@@ -117,7 +112,6 @@
 
 - [ ] Removals
   - [ ] `EventInterface`
-  - [ ] `EventManager`
   - [ ] `EventManagerInterface`
   - [ ] `EventManagerAwareInterface`
   - [ ] `EventManagerAwareTrait`

src/EventDispatchingInterface.php

@@ -0,0 +1,16 @@
+<?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;
+
+interface EventDispatchingInterface
+{
+    /**
+     * @return EventDispatcherInterface
+     */
+    public function getEventDispatcher();
+}