gitadora: show LEFT / RIGHT screens on sub screen in landscape mode (#900)

## Link to GitHub Issue or related Pull Request, if one exists
Continues #899 

## Description of change
#899 added the ability to display the gitadora subscreen in lanscape
mode with black bars on the side. With the new option the black bars can
instead display the LEFT / RIGHT screens, completing the two-monitor
full screen use case for arena model.

## Testing

src/spice2x/launcher/options.h

@@ -122,6 +122,7 @@ namespace launcher {
             GitaDoraSubOverlaySize,
             GitaDoraArenaSingleWindow,
             GitaDoraArenaWindowLayout,
+            GitaDoraArenaSubLayout,
             GitaDoraArenaAsioDriver,
             GitaDoraArenaRealtekAccess,
             LoadJubeatModule,
@@ -324,7 +325,6 @@ namespace launcher {
             OBSWebSocketDebug,
             ScreenshotIncludeOverlay,
             ScreenshotSubscreens,
-            GitaDoraSubscreenLandscape
         };
 
         enum class OptionsCategory {