[proposal] Add full screen support

[Kashouryo]

This is a very impressive plugin, and I had a lot of fun with it! However, if the preview has the full-screen feature, it can even be used as a screen saver.

[Malacath-92]

I took a closer look at this, and from what I can see there is no good way of doing this with the current bundled version of electron. The associated chrome version is quite old and doesn't support the standard web API for fullscreen and the webkit API doesn't work properly from my tests. And even if that is based on my mistake, I think it makes more sense to wait for the next bump in the electron version and try working with that.

Even then, it could still be that VSCode blocks fullscreen on the Webview panels, if that will be the case in the future I will talk with the devs and see what they are thinking.

[Malacath-92]

Small update: With the newest version of VSC using the standardized fullscreen api just results in the VSC window to be fullscreen, not the webview itself. So this still doesn't look doable.