Integrate go-webview2

[kjk]

webview control would be very useful.

Most of the work has already been done in https://github.com/jchv/go-webview2 (and wails fork https://github.com/wailsapp/go-webview2).

This is about providing built-in ctl_WebView.go based on that code.

The project is complete and pretty dormant so it would make sense to make the code part of this repo.

There are also fixes in forks that could be reviewed: https://github.com/jchv/go-webview2/network

[Mr-XiaoLei]

A built-in browser can be encapsulated！