Add drag and drop support

[jnschulze]

It looks like WebView2 will get drag and drop support for composition mode soon. -> make use of that API.

[chongbo2013]

Excuse me, if there is no problem in the environment system where webview2 is not installed, or whether it is possible to integrate the webview2 runtime environment into the package @jnschulze

[chongbo2013]

Windows 10 SDK 1903+（10.0.18362.1） What if it is below this version, support

[chongbo2013]

how to flutter call js and js call flutter thank u.

[toannguyendts]

To call JS you can use: _windowWVController.executeScript("console.log('Hello javascript')")

JS--> FLutter

1. In flutter, you must listen messages on stream _windowWVController.webMessage.listen((event) { /// Receive message from Webview print("On Message from Window Webview : " + event); });
2. In your HTML : window.chrome.webview.postMessage("Ahihi, Hello flutter");

[cacard]

so, now not support drag and drop event?