Allow changing Window.fullscreen and Window.borderless options after setup on iOS

[misl6]

Maintainer merge checklist

• Title is descriptive/clear for inclusion in release notes.
• Applied a Component: xxx label.
• Applied the api-deprecation or api-break label.
• Applied the release-highlight label to be highlighted in release notes.
• Added to the milestone version it was merged into.
• Unittests are included in PR.
• Properly documented, including versionadded, versionchanged as needed.

As pointed out by a user on Discord, currently we did not allow to switch between fullscreen and windowed mode on iOS programmatically, but only during startup.

After some tests, looks like this is feasible and doesn't generate any unexpected behavior (like the issue described in #2710, referring to commit c80cbd8)

I've also added some extra docs, explaining how to show / hide the status bar, as fullscreen alone is not enough to control the status bar visibility.

Window.fullscreen = True and Window.borderless = True:

Window.fullscreen = False and Window.borderless = False: