Feature Request: Lightgun support (XG-1)

[KremlingKuthroat19]

For the Atari XEGS games that are compatible with this core, there were a few games that used the XG-1 lightgun: https://en.wikipedia.org/wiki/Atari_XG-1_light_gun. This is the same lightgun that was used for the Atari 7800. This'd be a really cool feature to have to add more lightgun support to MiSTer :)

[RetroInVitro]

I support this request. SNAC support on the 7800/2600 core is fantastic. It lets you use the native XG-1 light gun as well as switching pins to allow the use of the Sega Phaser light gun as well since they're similar devices but with diff pin mappings.