event: modernize property declarations where possible

only private fields are modified; protected ones can't be changed in case someone extended the classes

src/event/entity/EntityMotionEvent.php

@@ -34,12 +34,11 @@ use pocketmine\math\Vector3;
 class EntityMotionEvent extends EntityEvent implements Cancellable{
 	use CancellableTrait;
 
-	/** @var Vector3 */
-	private $mot;
-
-	public function __construct(Entity $entity, Vector3 $mot){
+	public function __construct(
+		Entity $entity,
+		private Vector3 $mot
+	){
 		$this->entity = $entity;
-		$this->mot = $mot;
 	}
 
 	public function getVector() : Vector3{