Add MSAA sample count support thru RenderPipelineSettings

RenderPipelineSettings owns the global MSAA sample count level.  Each camera can control whether MSAA is supported or not, and if the camera's FrameSettings enable MSAA, then it will use the RenderPipelineSettings value for MSAA sample count.

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Camera/HDCamera.cs

             if (frameSettings.enableMSAA)
             {
                 // this is already pre-validated to be a valid sample count by InitializeFrameSettings
-                var sampleCount = QualitySettings.antiAliasing;
+                var sampleCount = (int)frameSettings.msaaSampleCount; 
                 tempDesc.msaaSamples = sampleCount;
             }
             else

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/RenderLoopSettings/RenderPipelineSettingsUI.cs

             EditorGUILayout.PropertyField(d.supportSSR, _.GetContent("Support SSR"));
             EditorGUILayout.PropertyField(d.supportSSAO, _.GetContent("Support SSAO"));
             EditorGUILayout.PropertyField(d.supportDBuffer, _.GetContent("Support Decal Buffer"));
-            EditorGUILayout.PropertyField(d.supportMSAA, _.GetContent("Support MSAA"));
+            EditorGUILayout.PropertyField(d.msaaSampleCount, _.GetContent("MSAA Sample Count"));
             EditorGUILayout.PropertyField(d.supportSubsurfaceScattering, _.GetContent("Support Subsurface Scattering"));
             --EditorGUI.indentLevel;
         }

ScriptableRenderPipeline/HDRenderPipeline/HDRP/Editor/RenderLoopSettings/SerializedRenderPipelineSettings.cs

         public SerializedProperty supportSSR;
         public SerializedProperty supportSSAO;
         public SerializedProperty supportDBuffer;
-        public SerializedProperty supportMSAA;
+        public SerializedProperty msaaSampleCount;
         public SerializedProperty supportSubsurfaceScattering;
 
         public SerializedGlobalLightLoopSettings lightLoopSettings;
             supportSSR = root.Find((RenderPipelineSettings s) => s.supportSSR);
             supportSSAO = root.Find((RenderPipelineSettings s) => s.supportSSAO);
             supportDBuffer = root.Find((RenderPipelineSettings s) => s.supportDBuffer);
-            supportMSAA = root.Find((RenderPipelineSettings s) => s.supportMSAA);
+            msaaSampleCount = root.Find((RenderPipelineSettings s) => s.msaaSampleCount);
             supportSubsurfaceScattering = root.Find((RenderPipelineSettings s) => s.supportSubsurfaceScattering);
 
             lightLoopSettings = new SerializedGlobalLightLoopSettings(root.Find((RenderPipelineSettings s) => s.lightLoopSettings));

ScriptableRenderPipeline/HDRenderPipeline/HDRP/RenderPipeline/FrameSettings.cs

         public bool enableTransparentObjects = true;
 
         public bool enableMSAA = false;
+        public MSAASamples msaaSampleCount { get; private set; }
 
         public bool enableShadowMask = false;
 
             aggregate.enableOpaqueObjects = srcFrameSettings.enableOpaqueObjects;
             aggregate.enableTransparentObjects = srcFrameSettings.enableTransparentObjects;
 
-            aggregate.enableMSAA = srcFrameSettings.enableMSAA && renderPipelineSettings.supportMSAA;
-            if (QualitySettings.antiAliasing < 1)
-                aggregate.enableMSAA = false;
+            aggregate.enableMSAA = srcFrameSettings.enableMSAA && ((int)renderPipelineSettings.msaaSampleCount > 1);
+            aggregate.msaaSampleCount = aggregate.enableMSAA ? renderPipelineSettings.msaaSampleCount : MSAASamples.None;
+
             aggregate.ConfigureMSAADependentSettings();
 
             aggregate.enableShadowMask = srcFrameSettings.enableShadowMask && renderPipelineSettings.supportShadowMask;

ScriptableRenderPipeline/HDRenderPipeline/HDRP/RenderPipeline/RenderPipelineSettings.cs

 
         // Engine
         public bool supportDBuffer = false;
-        public bool supportMSAA = false;
+        public MSAASamples msaaSampleCount = MSAASamples.None;
 
         public GlobalLightLoopSettings  lightLoopSettings = new GlobalLightLoopSettings();
         public ShadowInitParameters     shadowInitParams = new ShadowInitParameters();