Allow WKWebView to go fullscreen

[jsonfry]

To support things like YouTube video embeds going fullscreen.

The built in behavoiur for multiple windows / monitors is pretty good, here's a video of it in action:

full.screen.webview.xq29.mp4

[jsonfry]

This possibly resolves #553 and #3206

[brentsimmons]

Are there any risks to this? Side effects or edge cases?

What happens when a person doesn't have spaces turned on and it goes fullscreen? Is it obvious how to get out of fullscreen?

[jsonfry]

Thanks for looking at this, I really appreciate it.

In terms obviousness of getting out of fullscreen, it depends on the contents of the webpage that has asked to go fullscreen, but you can always move the mouse pointer to the top of the screen:

I think side effects and risks are minimal as WKWebView handles it all for you, it should behave the same as Safari. E.g. you see the same "Click to Exit Full Screen" behaviour in Safari:

Also, given the built-in web rules, content can't go fullscreen unless the action happens from direct user input (like a click), so there's the same risk level as a web browser in terms of malicious web content.

I've also tested what happens if you have content in fullscreen and then switch to another feed or entry, and that behaves correctly.

I couldn't work out how to turn off spaces in Sequoia or Tahoe (the two Macs I have here), I'd hope that WKWebView would use whatever OS fullscreen api is available or report to the web content that fullscreen is not available, but that could be an interesting thing to check if anyone else can?

This is a feed I've checked: https://www.henrikkarlsson.xyz/feed . The entry "Differently Free" has an embedded YouTube video that works (quite why that embed doesn't have the "Error 153" problem in #4860 I don't know).