[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.

plugins/RepeatNote/Entity/NoteRepeat.php

@@ -132,27 +132,6 @@ class NoteRepeat extends Entity
         );
     }
 
-    /**
-     * @see Entity->getNotificationTargetIds
-     */
-    public function getNotificationTargetIds(array $ids_already_known = [], ?int $sender_id = null, bool $include_additional = true): array
-    {
-        if (!\array_key_exists('object', $ids_already_known)) {
-            $target_ids = Note::getById($this->getNoteId())->getNotificationTargetIds();
-        } else {
-            $target_ids = $ids_already_known['object'];
-        }
-
-        // Additional actors that should know about this
-        if ($include_additional && \array_key_exists('additional', $ids_already_known)) {
-            array_push($target_ids, ...$ids_already_known['additional']);
-        } else {
-            return $target_ids;
-        }
-
-        return array_unique($target_ids);
-    }
-
     public static function schemaDef(): array
     {
         return [