graphics: custom full screen resolution (#274)

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

## Description of change
Adds a new option to forcibly set the full screen resolution.

Same idea as -windowscale.

## Compiling
🔺 

## Testing
Seems to be showing similar results as -windowscale:

* Works GREAT for IIDX/SDVX
* popn launches at correct resolution but only draws a small image (at
native res) - can be scaled with F11 menu
* nostalgia is broken in weird ways, image is drawn correctly but bottom
`credits` text draws at wrong offset, game's wintouch logic broken
(perhaps expectedly)

## Other notes
In theory this could enable "play sdvx in landscape mode" option but the
image scaling doesn't quite work with extreme values.

src/spice2x/launcher/options.h

@@ -27,8 +27,9 @@ namespace launcher {
             CaptureCursor,
             ShowCursor,
             DisplayAdapter,
-            GraphicsForceRefresh,
             GraphicsForceSingleAdapter,
+            GraphicsForceRefresh,
+            FullscreenResolution,
             Graphics9On12,
             spice2x_Dx9On12,
             NoLegacy,