Restore fullscreen toggle menu for the Android editor and clean up the immersive mode logic

[m4gr3d]

While testing #94285, I noticed a couple things:

• The diff was using an editor setting to enable immersive mode which required restarting the editor

  • I found that odd since Android apps are able to toggle immersive mode on/off without restarting themselves, so I updated the logic to allow toggling immersive mode on/off without having to restart the editor
  • In the process, I updated the immersive mode logic to reflect the latest best practices and removed the deprecated apis

• Looking for a way to expose the new immersive mode logic in the editor, I found out that the editor has a Toggle fullscreen menu which was disabled for Android (by me :) ) when the Android editor was first released

  • I restored the menu for the Android editor and wired the Android logic to toggle immersive mode. The new functionality can be seen in the video

Screen_Recording_20240828_030935.mp4

Note:

• The new Android immersive mode logic is hooked to the DisplayServer#window_set_mode(...) and DisplayServer#window_get_mode(....) apis which means that game logic can also leverage the new functionality to query and toggle immersive mode at runtime on Android
• The editor's immersive mode state is not used for the play / game window. This is done intentionally to allow the game logic to control the play / game window's immersive mode state via the DisplayServer apis
• The editor retains its immersive mode state when the project is reloaded, when the editor quit to the project manager or when a new project is loaded from the project manager that doesn't have its own editor layout config
• The editor's immersive mode state is not retained across full restart (killing and starting again) of the editor

Supersedes #94285

[akien-mga]

The new Android immersive mode logic is hooked to the DisplayServer#window_set_mode(...) and DisplayServer#window_get_mode(....) apis which means that game logic can also leverage the new functionality to query and toggle immersive mode at runtime on Android

I'm not too familiar with immersive mode on Android, but I assume that this might change the default behavior for a number of games that might be configured to be fullscreen by default, and end up immersive on Android. Would that reasonably be desired/intended behavior in this case? Or would that break compat if prior to this, it would not be immersive?

Might also be worth adding a note in the documentation of window_set_mode to clarify that it does this on Android.

[akien-mga]

Thanks!