Add new maxTilesLoading option to ol/PluggableMap

To be able to set the maximum number of currently loading tiles.

externs/olx.js

@@ -3649,6 +3649,7 @@ olx.layer.TileOptions.prototype.zIndex;
  *     map: (ol.PluggableMap|undefined),
  *     declutter: (boolean|undefined),
  *     style: (ol.style.Style|Array.<ol.style.Style>|ol.StyleFunction|undefined),
+ *     maxTilesLoading: (number|undefined),
  *     updateWhileAnimating: (boolean|undefined),
  *     updateWhileInteracting: (boolean|undefined),
  *     visible: (boolean|undefined),
@@ -3763,6 +3764,12 @@ olx.layer.VectorOptions.prototype.declutter;
 olx.layer.VectorOptions.prototype.style;
 
 
+/**
+ * Maximum number tiles to load simultaneously.  Default is `16`.
+ * @type {number|undefined}
+ */
+olx.layer.VectorOptions.prototype.maxTilesLoading;
+
 /**
  * When set to `true`, feature batches will be recreated during animations.
  * This means that no vectors will be shown clipped, but the setting will have a