Sanitizer fixes (#2280)

include/mbgl/mtl/mtl_fwd.hpp

@@ -3,10 +3,11 @@
 // Forward-declarations for metal-cpp types, allowing
 // references without including any third-party headers
 
-#include <memory>
+#include <cstdint>
 
 namespace CA {
 class MetalDrawable;
+class MetalLayer;
 } // namespace CA
 
 namespace NS {
@@ -39,7 +40,9 @@ class VertexDescriptor;
 
 namespace mbgl {
 namespace mtl {
+
 using CAMetalDrawablePtr = NS::SharedPtr<CA::MetalDrawable>;
+using CAMetalLayerPtr = NS::SharedPtr<CA::MetalLayer>;
 
 using MTLBlitCommandEncoderPtr = NS::SharedPtr<MTL::BlitCommandEncoder>;
 using MTLBlitPassDescriptorPtr = NS::SharedPtr<MTL::BlitPassDescriptor>;

include/mbgl/style/layers/mtl/custom_layer_render_parameters.hpp

@@ -1,8 +1,8 @@
 #pragma once
 
 #include <mbgl/style/layers/custom_layer_render_parameters.hpp>
-
 #include <mbgl/mtl/mtl_fwd.hpp>
+
 #include <Foundation/Foundation.hpp>
 #include <Metal/Metal.hpp>