graphics: option to change monitor resolution (#689)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
Add a new option under `Monitor` group to change the monitor resolution
before booting the game, very similar to how orientation / refresh rate
options work.

This would be useful for games like Polaris Chord that boots at current
resolution but manages to have graphical issues when not in 1080p.

## Testing

src/spice2x/launcher/options.h

@@ -199,6 +199,7 @@ namespace launcher {
             LoadStubs,
             AdjustOrientation,
             spice2x_AutoOrientation,
+            ChangeResolution,
             LogLevel,
             EAAutomap,
             EANetdump,