Add BC layer for notification blueprints

This gives extension authors time to add the new `getAttributes()`
method to their `BlueprintInterface` implementations.

The layer itself is easy to remove in beta.14.

src/Notification/Blueprint/AbstractBlueprint.php

@@ -1,23 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * For detailed copyright and license information, please view the
- * LICENSE file that was distributed with this source code.
- */
-
-namespace Flarum\Notification\Blueprint;
-
-abstract class AbstractBlueprint implements BlueprintInterface
-{
-    public function getAttributes(): array
-    {
-        return [
-            'type' => static::getType(),
-            'from_user_id' => ($fromUser = $this->getFromUser()) ? $fromUser->id : null,
-            'subject_id' => ($subject = $this->getSubject()) ? $subject->getKey() : null,
-            'data' => ($data = $this->getData()) ? json_encode($data) : null
-        ];
-    }
-}

src/Notification/Blueprint/BlueprintInterface.php

@@ -22,6 +22,7 @@ interface BlueprintInterface
     /**
      * Get the user that sent the notification.
      *
+     * @deprecated Will be removed for beta.14
      * @return User|null
      */
     public function getFromUser();
@@ -29,6 +30,7 @@ interface BlueprintInterface
     /**
      * Get the model that is the subject of this activity.
      *
+     * @deprecated Will be removed for beta.14
      * @return AbstractModel|null
      */
     public function getSubject();
@@ -36,10 +38,19 @@ interface BlueprintInterface
     /**
      * Get the data to be stored in the notification.
      *
+     * @deprecated Will be removed for beta.14
      * @return array|null
      */
     public function getData();
 
+    /**
+     * Get the attributes that uniquely identify a notification, plus metadata.
+     * TODO: Uncomment this for beta.14.
+     *
+     * @return array
+     */
+    //public function getAttributes(): array;
+
     /**
      * Get the serialized type of this activity.
      *