feat(ImageSet): Avoid exposing the images field by adding a getNumImagesMethod (#3179)

platform/core/src/classes/ImageSet.js

@@ -56,6 +56,8 @@ class ImageSet {
     }
   }
 
+  getNumImages = () => this.images.length
+
   getImage(index) {
     return this.images[index];
   }