Function hmrSetup

Code for injecting into subapp declaring JS module to enable hot module reloading

The code will use webpack's module.hot.accept API to add acceptance hook for a import JS module.

The webpack plugin in plugins/subapp-plugin.ts will inject this code when it detect a JS module declares subapps.

Remarks

the plugin will use the code from toString of this function to inject the code, so this function cannot have any external dependencies.