Bring back T4 templating service for tt files (#32172)

Author: ViktorHofer

src/coreclr/src/System.Private.CoreLib/System.Private.CoreLib.csproj

@@ -447,6 +447,11 @@
   <PropertyGroup>
     <FeatureAsyncCausalityTracer Condition="'$(FeatureCominterop)' == 'true'">true</FeatureAsyncCausalityTracer>
   </PropertyGroup>
+  
+  <ItemGroup>
+    <!-- This is the T4 template service and is added by VS anytime you modify a T4 template. Required for .tt files. -->
+    <Service Include="{508349b6-6b84-4df5-91f0-309beebad82d}" />
+  </ItemGroup>
 
   <!-- Setup ILLink.targets -->
   <ItemGroup>