Include extensions ref assemblies if used

Author: John Luo

src/Framework/ref/Microsoft.AspNetCore.App.Ref.csproj

@@ -110,14 +110,22 @@ This package is an internal implementation of the .NET Core SDK and is not meant
     </ItemGroup>
 
     <JoinItems Left="@(ReferencePathWithRefAssemblies)" Right="@(_AvailableExtensionsRefAssemblies)" LeftKey="Filename" RightKey="Filename" ItemSpecToUse="Left">
+      <Output TaskParameter="JoinResult" ItemName="_ReferencedExtensionsRefAssemblies" />
+    </JoinItems>
+
+    <JoinItems Left="@(_ReferencedExtensionsRefAssemblies)" Right="@(ExternalAspNetCoreAppReference)" LeftKey="Filename" RightKey="Identity" ItemSpecToUse="Left">
+      <Output TaskParameter="JoinResult" ItemName="_SelectedExtensionsRefs" />
+    </JoinItems>
+
+    <JoinItems Left="@(ReferencePathWithRefAssemblies)" Right="@(_SelectedExtensionsRefs)" LeftKey="Filename" RightKey="Filename" ItemSpecToUse="Left">
       <Output TaskParameter="JoinResult" ItemName="_SelectedExtensionsRefAssemblies" />
     </JoinItems>
 
     <ItemGroup>
       <AspNetCoreReferenceAssemblyPath
           Include="@(ReferencePathWithRefAssemblies)"
           Exclude="
-            @(_SelectedExtensionsRefAssemblies);
+            @(_ReferencedExtensionsRefAssemblies);
             @(ReferencePathWithRefAssemblies->WithMetadataValue('NuGetPackageId', 'Microsoft.NETCore.App.Ref'));
             @(ReferencePathWithRefAssemblies->WithMetadataValue('IsReferenceAssembly', 'false'));
             @(ReferencePathWithRefAssemblies->WithMetadataValue('ReferenceGrouping', 'Microsoft.NETCore.App'));" />