FUTDC support for CopyToOutputDirectory="IfDifferent"

src/Microsoft.VisualStudio.ProjectSystem.Managed.VS/ProjectSystem/VS/Rules/CopyToOutputDirectoryItem.xaml

@@ -16,6 +16,7 @@
     <EnumValue Name="Never" />
     <EnumValue Name="Always" />
     <EnumValue Name="PreserveNewest" />
+    <EnumValue Name="IfDifferent" />
   </EnumProperty>
 
   <BoolProperty Name="BuildAccelerationOnly"

src/Microsoft.VisualStudio.ProjectSystem.Managed.VS/ProjectSystem/VS/UpToDate/BuildUpToDateCheck.CopyType.cs

@@ -10,6 +10,7 @@ internal sealed partial class BuildUpToDateCheck
     internal enum CopyType
     {
         PreserveNewest,
+        IfDifferent,
         Always
     }
 }

src/Microsoft.VisualStudio.ProjectSystem.Managed.VS/ProjectSystem/VS/UpToDate/BuildUpToDateCheck.cs

@@ -797,6 +797,7 @@ private bool CheckCopyToOutputDirectoryItems(Log log, UpToDateCheckImplicitConfi
                 switch (copyType)
                 {
                     case CopyType.Always:
+                    case CopyType.IfDifferent:
                     {
                         // We have already validated the presence of these files, so we don't expect these to return
                         // false. If one of them does, the corresponding size would be zero, so we would schedule a build.

src/Microsoft.VisualStudio.ProjectSystem.Managed.VS/ProjectSystem/VS/UpToDate/CopyItem.cs

@@ -69,7 +69,12 @@ static BuildUpToDateCheck.CopyType ParseCopyType(string value)
                 return BuildUpToDateCheck.CopyType.PreserveNewest;
             }
 
-            throw Assumes.Fail($"CopyToOutputDirectory should be Always or PreserveNewest, not {value}");
+            if (string.Equals(value, CopyToOutputDirectoryItem.CopyToOutputDirectoryValues.IfDifferent, StringComparisons.PropertyLiteralValues))
+            {
+                return BuildUpToDateCheck.CopyType.IfDifferent;
+            }
+
+            throw Assumes.Fail($"CopyToOutputDirectory should be Always, PreserveNewest or IfDifferent, not {value}");
         }
     }