Fix wireframe depth gradient on Vulkan

Source/Shaders/Quad.shader

@@ -149,6 +149,9 @@ float4 PS_Wireframe(float4 SvPosition : SV_Position) : SV_Target0
 {
     // Depth-based gradient
     float alpha = saturate(SvPosition.w * UNITS_TO_METERS_SCALE * 0.1f);
+#if VULKAN
+    alpha = 1 - alpha;
+#endif
     return lerp(ColorNear, ColorFar, alpha);
 }