Include all .xml files in targeting pack (#26147)

* Include all .xml files in targeting pack

* Better syntax

* Remove distinct

Author: wtgodbe

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

@@ -143,6 +143,10 @@ This package is an internal implementation of the .NET Core SDK and is not meant
       <AspNetCoreReferenceDocXml Include="@(_ResolvedProjectReferencePaths->'%(RootDir)%(Directory)%(FileName).xml')"
           Condition="Exists('%(RootDir)%(Directory)%(FileName).xml')" />
       <AspNetCoreReferenceDocXml Include="@(_SelectedExtensionsRefAssemblies->'$(RuntimeExtensionsReferenceDirectory)%(FileName).xml')" />
+      <!-- Grab remaining .xml files from packages -->
+      <AspNetCoreReferenceDocXml 
+          Include="@(AspNetCoreReferenceAssemblyPath->WithMetadataValue('ExternallyResolved', 'true')->'%(RootDir)%(Directory)%(Filename).xml')" 
+          Condition="Exists('%(RootDir)%(Directory)%(Filename).xml')" />
 
       <RefPackContent Include="@(AspNetCoreReferenceAssemblyPath)" PackagePath="$(RefAssemblyPackagePath)" />
       <RefPackContent Include="@(AspNetCoreReferenceDocXml)" PackagePath="$(RefAssemblyPackagePath)" />