Add support for additional display modes

[falbrechtskirchinger]

Implement additional display modes in SDL2 and WinAPI backends:

• Windowed fullscreen
• Windowed (non-resizable)

Fixes #1512 Closes #1615

To-do:

• [ ] Rebase after #1612.
• [ ] Rework options screen and in-game settings window.

Notes and references:

• https://learn.microsoft.com/en-us/windows/win32/winmsg/window-styles
• https://src.chromium.org/viewvc/chrome/trunk/src/ui/views/win/fullscreen_handler.cc

[falbrechtskirchinger]

@Spikeone There you go!