NamcoGuncon: Add an option to scale X coordinates

Fixes what appears to be curvature correction at the edges of the
screen.

src/core/gpu.h

@@ -154,7 +154,8 @@ public:
   static std::unique_ptr<GPU> CreateSoftwareRenderer();
 
   // Converts window coordinates into horizontal ticks and scanlines. Returns false if out of range. Used for lightguns.
-  bool ConvertScreenCoordinatesToBeamTicksAndLines(s32 window_x, s32 window_y, u32* out_tick, u32* out_line) const;
+  bool ConvertScreenCoordinatesToBeamTicksAndLines(s32 window_x, s32 window_y, float x_scale, u32* out_tick,
+                                                   u32* out_line) const;
 
   // Returns the video clock frequency.
   TickCount GetCRTCFrequency() const;