修复了某些异常、更新了部分语法

AppScope/app.json5

@@ -4,7 +4,7 @@
     "vendor": "example",
     "versionCode": 1000000,
     "versionName": "1.0.0",
-    "icon": "$media:app_icon",
+    "icon": "$media:layered_image",
     "label": "$string:app_name"
   }
 }

AppScope/resources/base/media/layered_image.json

@@ -0,0 +1,7 @@
+{
+  "layered-image":
+  {
+    "background" : "$media:background",
+    "foreground" : "$media:foreground"
+  }
+}