[COMPONENT][Notification] Make logic more generic and robust

Fixed various bugs

Some important concepts to bear in mind:

* Notification: Associated with activities, won't be reconstructed
together with objects, can be thought of as transient

* Attention: Associated with objects, will be reconstructed with them, can
be thought as persistent

* Notifications and Attentions have no direct implications.

* Mentions are a specific form of attentions in notes, leads to the creation of Attentions.

Finally,

Potential PHP issue detected and reported: https://github.com/php/php-src/issues/8199
`static::method()` from a non static context (such as a class method) calls `__call`, rather than
the expected `__callStatic`. Can be fixed by using `(static fn() => static::method())()`, but the
usage of the magic method is strictly unnecessary in this case.

components/Group/Group.php

@@ -51,12 +51,17 @@ class Group extends Component
      * Enqueues a notification for an Actor (such as person or group) which means
      * it shows up in their home feed and such.
      */
-    public function onNewNotificationWithTargets(Actor $sender, Activity $activity, array $targets = [], ?string $reason = null): bool
+    public function onNewNotificationStart(Actor $sender, Activity $activity, array $targets = [], ?string $reason = null): bool
     {
         foreach ($targets as $target) {
             if ($target->isGroup()) {
                 // The Group announces to its subscribers
-                Notification::notify($target, $activity, $target->getSubscribers(), $reason);
+                Notification::notify(
+                    sender: $target,
+                    activity: $activity,
+                    targets: $target->getSubscribers(),
+                    reason: $reason,
+                );
             }
         }