graphics: custom resolution for subscreen (#553)

## Link to GitHub Issue, if one exists
n/a

## Description of change
Allow user to specify a custom resolution for the sub monitor, in
addition to the existing refresh rate option

This would allow practically any touch monitor (including ones with
weird resolution / aspect ratio / refresh rate) to be used with
IIDX/SDVX.

## Testing
Tested with various resolution / refresh rate combinations on IIDX /
SDVX.

src/spice2x/launcher/options.h

@@ -31,6 +31,7 @@ namespace launcher {
             GraphicsForceRefresh,
             FullscreenResolution,
             FullscreenOrientationFlip,
+            FullscreenSubResolution,
             FullscreenSubRefreshRate,
             Graphics9On12,
             spice2x_Dx9On12,
@@ -85,11 +86,11 @@ namespace launcher {
             SDVXPrinterJPGQuality,
             SDVXDisableCameras,
             SDVXNativeTouch,
+            spice2x_SDVXSubRedraw,
             spice2x_SDVXDigitalKnobSensitivity,
             SDVXDigitalKnobSocd,
             spice2x_SDVXAsioDriver,
             spice2x_SDVXSubPos,
-            spice2x_SDVXSubRedraw,
             LoadDDRModule,
             DDR43Mode,
             DDRSkipCodecRegisteration,