`tns migrate` clears the platforms and next build fails if a custom android runtime was used

If tns migrate was ran on an app with a custom android runtime (tns platform add android --frameworkPath /test/runtime.tgz), next build would fail. This is because the platforms/android folder is deleted and the version of the tns-android package was previously set in the package.json to the literal next version of the runtime. This runtime, of course, couldn't be found in npm and thus the build fails. Couldn't runtimes added with --frameworkPath be handled differently and in some way marked as such in the package.json? Also, couldn't a simple gradlew clean do the dirty work instead of deleting the whole platforms folder?

首先跟踪 tns migrate 的入口点及其对 --frameworkPath 的处理，然后检查 package.json 如何记录 tns-android 的版本，以及如何删除 platforms/android。将该行为与提到的 gradlew clean 选项进行比较。当迁移使用自定义 runtime 的应用能够保留可用的 runtime 引用，并且下一次构建成功时，即表示完成。