Remove Android's white background color in UnityWidgetController.kt

Author: timbotimbo

android/src/main/kotlin/com/xraph/plugin/flutter_unity_widget/FlutterUnityWidgetController.kt

@@ -57,7 +57,7 @@ class FlutterUnityWidgetController(
         if (context != null) tempContext = context
         // set layout view
         view = FrameLayout(tempContext)
-        view.setBackgroundColor(Color.WHITE)
+        view.setBackgroundColor(Color.TRANSPARENT)
 
         // setup method channel
         methodChannel = MethodChannel(binaryMessenger, "plugin.xraph.com/unity_view_$id")