Add fullscreen (and renderer) toggle & make windowed mode use a separate resolution

Changes in this branch:

• F11 now changes between fullscreen and windowed mode, instead of changing brightness.
• F10 now changes between renderers, instead of quitting the game. (Just use Alt + F4 if you need a shortcut to quit, it's faster too)
• To make the fullscreen toggle more useful, windowed mode now uses a separate resolution, set to 640x400 by default. Uses separate scr_width_w and scr_height_w cvars.
• The "Set Resolution..." menu has been updated.
  • Changes the default windowed resolution while in windowed mode.
  • The fullscreen toggle works inside this menu.
  • Backspace now also works in this menu, setting both fullscreen & windowed resolutions to their defaults (1280x800 and 640x400).
  • Invalid resolutions are displayed in red. When trying to switch to an invalid resolution, SRB2 will fall back on the base resolution (320x200).
• Removed unneeded M_CentreText function, since it was mainly used in the resolution menu, and replaced it with V_DrawCenteredString calls.
• Reduces clutter by resolution information in logs.
• Also contains the change made by !1733 (merged), since this modifies everything else in that same function already.

srb2win_fullscreen-toggle.exe - Updated 24/11/2022