Allow toggling fullscreen without restart and add keybind

[grorp]

Fixes #2732, opened in 2015, closed as non-trivial in 2017 (because there was no Irrlicht fork and no SDL device back then)

New users can easily think that the fullscreen setting is broken because it's only applied after a restart and this isn't even documented.

This PR allows toggling fullscreen via the settings menu without a restart. For convenience, there's also a new keybind called keymap_fullscreen (F11 by default). As a bonus, window_maximized is now applied immediately too.

To do

This PR is a Ready for Review.

How to test

Change the fullscreen and window_maximized settings. See that Minetest reacts immediately.

Press F11. See that fullscreen mode is toggled and that the fullscreen checkbox in the settings is updated too.

[rubenwardy]

This is much easier to implement now that we use borderless fullscreen

[grorp]

This is much easier to implement now that we use borderless fullscreen

What actually makes it much easier is that we now have an Irrlicht fork and the SDL device. Now that we have these two things, this PR automatically works with "real" fullscreen too if we tell SDL to enable it.

[sfan5]

Tested and mostly works, but:

• going in and out of fullscreen moves the window downwards by like 10 pixels (not our fault?)
• fullscreening a maximized window and returning will cause it to be unmaximized

[grorp]

going in and out of fullscreen moves the window downwards by like 10 pixels (not our fault?)

Cannot reproduce (Fedora 39 "Workstation", GNOME 45, Wayland). I think indeed not our fault.

fullscreening a maximized window and returning will cause it to be unmaximized

That should depend on your window_maximized setting, which is appplied again when leaving fullscreen. I could just remove that part. The setting and the actual state go out of sync anyway whenever you minimize/maximize the window.

[sfan5]

Cannot reproduce (Fedora 39 "Workstation", GNOME 45, Wayland). I think indeed not our fault.

Well I'm on X11, but I think the source of this behavior is more likely in SDL.

I could just remove that part. The setting and the actual state go out of sync anyway whenever you minimize/maximize the window.

👍