update local HLSL support file to match changes in Unity's copy. Metal was added to list of APIs that supported attenuateing using the red channel so this broke attenuation across the board

Assets/ScriptableRenderPipeline/MobileRenderPipeline/ClassicDeferred/HLSLSupport.cginc

 #define UNITY_POSITION(pos) float4 pos : SV_POSITION
 #endif
 
-#if defined(SHADER_API_D3D9) || defined(SHADER_API_D3D11) || defined(SHADER_API_D3D11_9X) || defined(SHADER_API_PSP2) || defined(SHADER_API_PSSL)
+#if defined(SHADER_API_D3D9) || defined(SHADER_API_D3D11) || defined(SHADER_API_D3D11_9X) || defined(SHADER_API_PSP2) || defined(SHADER_API_PSSL) || defined(SHADER_API_METAL)
 #define UNITY_ATTEN_CHANNEL r
 #else
 #define UNITY_ATTEN_CHANNEL a