Keyboard and Background Rendering Enhancements

- Adds background rendering mode, where Alt+Tabbing does not pause the game - Enabled by default, press Ctrl + Alt + Shift + B to toggle this - Adds left Alt and Ctrl key blocking - These keys alias to Insert and Delete in this game, and makes pressing them cycle UI pages... - The option to disable it is now offered (see `AgDrag.Keyboard` in `AgDrag.ini` for more details). - The command console (Ctrl + Shift + Tab if RTSS is installed) now blocks the game's keyboard input while active.

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IMPORTANT NOTE:

The background rendering feature is intended for windowed mode only. If you try to use it in fullscreen mode, chances are you will not be able to Alt+Tab back into the game.

This change is primarily designed to make the game compatible with Borderless Gaming or GeDoSaTo's Force Borderless Window option. Without the stuff that AgDrag does, keyboard and mouse input would continue being processed by the game while you were working in a different application.

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The standalone DLL contains an experimental map fix, it produces almost perfect results at 21:9 (if you ignore UI centering). It remains largely unusable at 16:3, however.