[7.x.x Backport] MSAA fix for Metal MacOS/Editor (#2417)

* Metal MacOS/Editor MSAA fix. Require an explicit MSAA resolve pass unless the platform is mobile

* Added changelog entry

Author: manuele-bonanno

com.unity.render-pipelines.universal/CHANGELOG.md

@@ -209,6 +209,7 @@ The version number for this package has increased due to a version update of a r
 - Fixed an issue where Normal Map Textures didn't apply when you added them to newly-created Materials. [case 1197217](https://issuetracker.unity3d.com/product/unity/issues/guid/1197217/)
 - Fixed an issue with deleting shader passes in the custom renderer features list [case 1201664](https://issuetracker.unity3d.com/issues/urp-remove-button-is-not-activated-in-shader-passes-list-after-creating-objects-from-renderer-features-in-urpassets-renderer)
 - Fixed an issue where particles had dark outlines when blended together [case 1199812](https://issuetracker.unity3d.com/issues/urp-soft-particles-create-dark-blending-artefacts-when-intersecting-with-scene-geometry)
+- Fixed MSAA on Metal MacOS and Editor.
 
 ## [7.1.6] - 2019-11-22
 

com.unity.render-pipelines.universal/Runtime/ForwardRenderer.cs

@@ -559,8 +559,11 @@ void SetupBackbufferFormat(int msaaSamples, bool stereo)
 
         bool PlatformRequiresExplicitMsaaResolve()
         {
+            // On Metal/iOS the MSAA resolve is done implicitly as part of the renderpass, so we do not need an extra intermediate pass for the explicit autoresolve.
+            // TODO: should also be valid on Metal MacOS/Editor, but currently not working as expected. Remove the "mobile only" requirement once trunk has a fix.
+
             return !SystemInfo.supportsMultisampleAutoResolve &&
-                   SystemInfo.graphicsDeviceType != GraphicsDeviceType.Metal;
+                   !(SystemInfo.graphicsDeviceType == GraphicsDeviceType.Metal && Application.isMobilePlatform);
         }
 
         /// <summary>