[Android] Playground源码需要写满注释

因为按照官网文档无法构建成功Android应用，所以还需要参考Playground里的源码自行修改构建，但是Playground里面的代码注释几乎没有，许多代码都无法知其准确用意。如：org/apache/weex/WXApplication.java onCreate() 方法中的这一句代码：WXSDKManager.getInstance().setAccessibilityRoleAdapter(new DefaultAccessibilityRoleAdapter());
请帮我解惑！谢谢！

Start with the Playground source file org/apache/weex/WXApplication.java, especially the onCreate() call to setAccessibilityRoleAdapter. Compare the code with the official Android build documentation and document the purpose of unclear code throughout the Playground; done means the relevant source has useful explanatory comments and the build guidance is understandable.

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