Specify a GUID for the IL SDK and expose it to slngen (#46877)

* Specify a GUID for the IL SDK and expose it to slngen

Author: ViktorHofer

eng/slngen.targets

@@ -10,4 +10,7 @@
     <!-- Include CompilerServices.Unsafe as it's a transitive test dependency. -->
     <IncludeInSolutionFile Condition="'$(IsNETCoreAppRef)' == 'true' and '$(MSBuildProjectName)' == 'System.Runtime.CompilerServices.Unsafe'">true</IncludeInSolutionFile>
   </PropertyGroup>
-</Project>
+  <ItemGroup>
+    <SlnGenCustomProjectTypeGuid Include=".ilproj" ProjectTypeGuid="{F571AB99-FB84-49F4-A0DF-F27AA55F3F3F}" />
+  </ItemGroup>
+</Project>

src/coreclr/.nuget/Microsoft.NET.Sdk.IL/targets/Microsoft.NET.Sdk.IL.targets

@@ -16,8 +16,16 @@ Copyright (c) .NET Foundation. All rights reserved.
     <DefaultLanguageSourceExtension>.il</DefaultLanguageSourceExtension>
     <Language>IL</Language>
     <TargetRuntime>Managed</TargetRuntime>
+    <DefaultProjectTypeGuid Condition="'$(DefaultProjectTypeGuid)' == ''">{F571AB99-FB84-49F4-A0DF-F27AA55F3F3F}</DefaultProjectTypeGuid>
+    <AppDesignerFolder Condition="'$(AppDesignerFolder)' == ''">Properties</AppDesignerFolder>
+    <AlwaysUseNumericalSuffixInItemNames>true</AlwaysUseNumericalSuffixInItemNames>
   </PropertyGroup>
 
+  <ItemGroup>
+    <ProjectCapability Include="Managed" />
+    <ProjectCapability Include="ReferencesFolder" />
+  </ItemGroup>
+
   <PropertyGroup>
     <_OSPlatform Condition="$([MSBuild]::IsOSPlatform('windows'))">win</_OSPlatform>
     <_OSPlatform Condition="$([MSBuild]::IsOSPlatform('linux'))">linux</_OSPlatform>