Merge pull request #12219 from ahocevar/object-properties

Add 'properties' to Layer constructors

src/ol/layer/Group.js

@@ -33,6 +33,7 @@ import {listen, unlistenByKey} from '../events.js';
  * @property {number} [maxZoom] The maximum view zoom level (inclusive) at which this layer will
  * be visible.
  * @property {Array<import("./Base.js").default>|import("../Collection.js").default<import("./Base.js").default>} [layers] Child layers.
+ * @property {Object<string, *>} [properties] Arbitrary observable properties. Can be accessed with `#get()` and `#set()`.
  */
 
 /**