fix: Object layer parsing for JSON format

- When loading in JSON from object layers didn't get parsed and where
empty
- Default values added for ellipse and point properties (as they might
not be present in JSON)

Author: JochenHeizmann

packages/tiled/lib/src/layer.dart

@@ -194,7 +194,12 @@ abstract class Layer {
             parser.getString('color', defaults: ObjectGroup.defaultColorHex);
         final color =
             parser.getColor('color', defaults: ObjectGroup.defaultColor);
-        final objects = parser.getChildrenAs('object', TiledObject.parse);
+
+        final objects = parser.formatSpecificParsing(
+          (json) => json.getChildrenAs('objects', TiledObject.parse),
+          (xml) => xml.getChildrenAs('object', TiledObject.parse),
+        );
+
         layer = ObjectGroup(
           id: id,
           name: name,

packages/tiled/lib/src/objects/tiled_object.dart

@@ -118,11 +118,11 @@ class TiledObject {
     );
 
     final ellipse = parser.formatSpecificParsing(
-      (json) => json.getBool('ellipse'),
+      (json) => json.getBool('ellipse', defaults: false),
       (xml) => xml.getChildren('ellipse').isNotEmpty,
     );
     final point = parser.formatSpecificParsing(
-      (json) => json.getBool('point'),
+      (json) => json.getBool('point', defaults: false),
       (xml) => xml.getChildren('point').isNotEmpty,
     );
     final text = parser.getSingleChildOrNullAs('text', Text.parse);