message: Fix compile warnings/errors in metal-cpp.h
  Forward declare MTL::Drawable to avoid conflicts. "Drawable" is a common type name
diff: @@ -4511,6 +4511,7 @@ _MTL_PRIVATE_DEF_SEL(writeMask,
  namespace MTL
  {
  +class Drawable;
  using DrawablePresentedHandler = void (^)(class Drawable*);
  using DrawablePresentedHandlerFunction = std::function<void(class Drawable*)>;
  