Made SDL_ReadSurfacePixel a public function

Fixes https://github.com/libsdl-org/SDL/issues/8320

src/dynapi/SDL_dynapi.sym

@@ -963,6 +963,7 @@ SDL3_0.0.0 {
     SDL_GetHapticFromInstanceID;
     SDL_GetHapticInstanceID;
     SDL_GetHapticName;
+    SDL_ReadSurfacePixel;
     # extra symbols go here (don't modify this line)
   local: *;
 };