macOS: fix colors appearing oversaturated on P3 displays.

The fix only applies to macOS 11+ when using OpenGL.

src/common/macos.h

@@ -26,6 +26,8 @@
 
 #include <string>
 
+typedef struct SDL_Window SDL_Window;
+
 namespace love
 {
 namespace macos
@@ -55,6 +57,12 @@ void requestAttention(bool continuous);
 void setMetalLayerVSync(void *metallayer, bool vsync);
 bool getMetalLayerVSync(void *metallayer);
 
+/**
+ * Explicitly sets the window's color space to be sRGB - which stops the OS
+ * from interpreting the backbuffer output as P3 on P3-capable displays.
+ **/
+void setWindowSRGBColorSpace(SDL_Window *window);
+
 } // macos
 } // love