feat: support devtools for better user experience

[await-ovo]

Feature Request

@harlan-zw Hi, first of all, it's nice to be able to use this plugin inside webpack, but it would be nice to be able to use design in devtools like vite.

I really like design in devtools and autocomplete, it is awesome!

So, I've tried to add a backend server to handle post requests from devtools. So far it's working ok in examples:

Just import "windi-devtools" or "virtual:windi-devtools" into your code and you can experience this very cool feature.

I also added a server user option to customize the host and port of the backend server, like following:

module.exports = {
  webpack: {
    plugins: {
      add: [
        new WindiCSSWebpackPlugin({
          virtualModulePath: 'src',
          server: {
            port: 9999,
            host: 'localhost'
          }
        })
      ],
    },
  }
}

Known Issues

• If you use eslint-webpack-plugin in your project, you need to configure it to ignore virtual:windi-devtools to avoid errors:

// craco.config.js
module.exports = {
  eslint: {
      pluginOptions: config => {
        config.exclude = ['**/node_modules/**', '**/virtual:windi-devtools*']
        return config;
      },
  }
}

• When use devtools in examples/umijs, the css does not change when I change the class attribute in browser, I am still looking for the reason.

• Currently the backend server does not support https

Finally, thank you very much for reading the content of this PR and the review :)

[harlan-zw]

This is really awesome, great job and thanks for the contribution 👏 @await-ovo!