`tns prepare ios --watch` does not "watch" the project/node_modules for changes

Environment
Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project):

• CLI: 6.0.2
• Cross-platform modules:
• Android Runtime:
• iOS Runtime:
• Plugin(s):

Describe the bug
Executing tns prepare ios --watch on a project compatible with 6.0.0, the project is correctly prepared but it is not being watched and making any changes to the app or node_modules folders does not trigger new prepare.

To Reproduce

• Make a new app using CLI
• Run `tns prepare ios --watch
• Wait for the project to prepare
• Make changes to the app folder or any nativescript plugin in node_modules
• The app is not re-prepared

Expected behavior
Using --watch watches the app and node_modules for changes

首先，在一个新的 CLI 兼容应用中运行 tns prepare ios --watch，观察 app 和 node_modules 目录下的更改是否会触发再次 prepare。跟踪 prepare ios 的 watch 入口点及其文件监视设置；当两个位置都能可靠地触发重新 prepare 时即表示完成。