Add LibraryImportGenerator to ref pack (#68247)

Author: elinor-fung

src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator/LibraryImportGenerator.csproj

@@ -21,6 +21,7 @@
     <PackageProjectUrl>https://github.com/dotnet/runtime/tree/main/src/libraries/System.Runtime.InteropServices/gen/LibraryImportGenerator</PackageProjectUrl>
     <Description>LibraryImportGenerator</Description>
     <PackageTags>LibraryImportGenerator, analyzers</PackageTags>
+    <IsNETCoreAppAnalyzer>true</IsNETCoreAppAnalyzer>
   </PropertyGroup>
 
   <ItemGroup>

src/libraries/System.Runtime.InteropServices/src/System.Runtime.InteropServices.csproj

@@ -51,4 +51,10 @@
   <ItemGroup>
     <ProjectReference Include="$(CoreLibProject)" />
   </ItemGroup>
+  <ItemGroup>
+    <!-- Add the source generator as an analyzer reference so that it gets included in the ref pack.
+         See https://github.com/dotnet/runtime/issues/61321 -->
+    <AnalyzerReference Include="..\gen\LibraryImportGenerator\LibraryImportGenerator.csproj" />
+  </ItemGroup>
+
 </Project>