Proposed demo: Fullscreen API

[KaliedaRik]

Proposal:
The Fullscreen API adds methods to present a specific Element (and its descendants) in fullscreen mode, and to exit fullscreen mode once it is no longer needed. This makes it possible to present desired content - such as an online game - using the user's entire screen, removing all browser user interface elements and other applications from the screen until fullscreen mode is shut off.

In our case the Element in question would be a <canvas> element. The demo would check to see if we can make a SC canvas fullscreen (following user interaction), and that the functionality, accessibility and UI of the canvas display remains unaffected by the canvas being made fullscreen.

Risks:
Browser support for this functionality seems to be good, with only Safari on iOS (specifically iPhone) holding out.

[KaliedaRik]

Implementing this functionality in a demo is fairly simple, with no changes required to the SC code base itself.

New demo DOM-018 created in the 2023-june-updates branch.