nost: touch piano mode (#830)

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

## Description of change
Touch piano mode. Allows piano keys to be played with the touch screen.
Since the touch screen is still needed for menu navigation (including
during songs) a toggle switch is added so that the user can flip between
navigation mode and piano mode.

The touch targets are pixel-perfect. Don't let the game's piano
animations fool you.

## Testing

src/spice2x/launcher/options.h

@@ -297,6 +297,7 @@ namespace launcher {
             DDRP4IOBufferMode,
             InputRequiresFocus,
             NostalgiaPoke,
+            NostalgiaTouchMode,
             ForceBackBufferCount,
             SDVXWindowedSubscreenSize,
             SDVXWindowedSubscreenPosition,