Merge pull request #12416 from ahocevar/eventtype-generics

Use generics to limit event types in on(), once() and un()

src/ol/Object.js

@@ -78,6 +78,8 @@ export class ObjectEvent extends Event {
  * object.unset('foo').
  *
  * @fires ObjectEvent
+ * @template {string} EventTypes
+ * @extends Observable<'propertychange'|EventTypes>
  * @api
  */
 class BaseObject extends Observable {