metal: add all the files

src/core/renderer_mtl/objc_helper.mm

@@ -0,0 +1,12 @@
+#include "renderer_mtl/objc_helper.hpp"
+
+// TODO: change the include
+#import <Metal/Metal.h>
+
+namespace Metal {
+
+dispatch_data_t createDispatchData(const void* data, size_t size) {
+    return dispatch_data_create(data, size, dispatch_get_global_queue(0, 0), ^{});
+}
+
+} // namespace Metal