Browser opens long before webpack is ready

Right now, running `ionic serve` will use the Angular CLI's dev server, which uses webpack-dev-server. As far as I know, there isn't a way (via child processes) to know when the bundles are ready, aside from maybe parsing stdout of the process. This results in the Ionic CLI opening the browser window much sooner than expected and displaying a white screen until webpack-dev-server finally compiles everything and loads the app.

This message is displayed when the window is opened:

```
[ng] ℹ ｢wdm｣: wait until bundle finished: /
```

The Angular CLI used to have the same behavior if `--open` is specified, but it seems like it was fixed as of version 6.

從啟動 Angular CLI 開發伺服器的 ionic serve 流程開始，檢查它如何決定何時開啟瀏覽器。將其就緒處理方式與 issue 中描述的 Angular CLI 行為進行比較。完成的標準是：瀏覽器在 webpack-dev-server 完成編譯後開啟，而不是在 bundle 仍在建置時顯示白畫面。

由索引模型根據 Issue 內容生成。