Added cross-browser fullscreen behaviour

[MarielaTihova]

Resolves #147

[MarielaTihova]

Slide effect

When you switch to full screen, a black page appears that slides to the left.

Screen.20Recording.202025-10-20.20at.2014.mp4
Screen capture test video: MacOS Sequoia 15.6.1 Safari 18.6

I have looked into this and it only happens when:

• Browser is Safari
• We have our browser on fullscreen mode already before clicking the fullscreen button. The difference is that once we have triggered the browser's native event for fullscreen (Ctrl + Command + F) and then trigger requestFullscreen(), Safari attempts to create a new OS-level fullscreen Space for the element, which causes the brief black flash/slide animation. This is expected behaviour in Safari/macOS and is not caused by the code we have in this repo.

There might be workarounds but they would require too much of a faking of fullscreen behaviour and I think it's not worth the trade-off.