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/CMakeLists.txt

@@ -417,6 +417,7 @@ set(SOURCE_FILES ${SOURCE_FILES}
         games/nost/nost.cpp
         games/nost/io.cpp
         games/nost/poke.cpp
+        games/nost/touch_mode.cpp
         games/gitadora/gitadora.cpp
         games/gitadora/asio.cpp
         games/gitadora/io.cpp
@@ -610,6 +611,7 @@ set(SOURCE_FILES ${SOURCE_FILES}
         overlay/windows/keypad.cpp
         overlay/windows/log.cpp
         overlay/windows/midi.cpp
+        overlay/windows/nostalgia_touch_piano.cpp
         overlay/windows/obs.cpp
         overlay/windows/obs_websocket.cpp
         overlay/windows/patch_manager.cpp