Update KnownILLinkPack/KnownILCompilerPack instead of using a PackageReference to Microsoft.DotNet.ILCompiler.

This uses the same mechanism that the repo already uses for updating the apphost/ref/runtime packs as well as the crossgen2 pack

Author: jkoritzinsky

eng/testing/linker/SupportFiles/Directory.Build.targets

@@ -1,18 +1,8 @@
 <Project>
-
-  <PropertyGroup>
-    <!-- Used to silence the warning caused by the workaround for https://github.com/dotnet/runtime/issues/81382 -->
-    <SuppressGenerateILCompilerExplicitPackageReferenceWarning>true</SuppressGenerateILCompilerExplicitPackageReferenceWarning>
-  </PropertyGroup>
-
-  <!-- needed to reference a specific version of NetCoreApp. Workaround https://github.com/dotnet/runtime/issues/81382 -->
   <ItemGroup>
     <FrameworkReference Update="Microsoft.NETCore.App"
                         RuntimeFrameworkVersion="$(MicrosoftNETCoreAppRefVersion)" />
 
-    <PackageReference Include="Microsoft.DotNet.ILCompiler"
-                      Version="$(MicrosoftNETCoreAppRefVersion)" />
-
     <!-- Workaround when there is no vNext SDK available; copy known packs info from 9.0. -->
     <KnownAppHostPack Include="@(KnownAppHostPack->WithMetadataValue('TargetFramework', 'net9.0'))"
                      TargetFramework="$(TargetFramework)"
@@ -64,6 +54,13 @@
       <AppHostRuntimeIdentifiers Condition=" '$(DotNetBuildSourceOnly)' == 'true' ">$(TargetRuntimeIdentifier)</AppHostRuntimeIdentifiers>
     </KnownRuntimePack>
 
+    <KnownILCompilerPack Update="Microsoft.DotNet.ILCompiler">
+      <ILCompilerPackVersion>$(MicrosoftNETCoreAppRefVersion)</ILCompilerPackVersion>
+    </KnownILCompilerPack>
+
+    <KnownILLinkPack Update="Microsoft.NET.ILLink.Tasks">
+      <ILLinkPackVersion>$(MicrosoftNETCoreAppRefVersion)</ILLinkPackVersion>
+    </KnownILLinkPack>
   </ItemGroup>
 
   <!--

eng/tools/GenerateFiles/Directory.Build.props.in

@@ -4,8 +4,5 @@
     <ArtifactsShippingPackagesDir>${ArtifactsShippingPackagesDir}</ArtifactsShippingPackagesDir>
     <TreatWarningsAsErrors Condition="'$(BuildingInsideVisualStudio)' != 'true'">true</TreatWarningsAsErrors>
     <LibNetHostAppPackVersion Condition=" '$(LibNetHostAppPackVersion)' == '' ">${LibNetHostAppPackVersion}</LibNetHostAppPackVersion>
-
-    <!-- Temporarily hardcoded to true -->
-    <SuppressGenerateILCompilerExplicitPackageReferenceWarning>true</SuppressGenerateILCompilerExplicitPackageReferenceWarning>
   </PropertyGroup>
 </Project>

eng/tools/GenerateFiles/Directory.Build.targets.in

@@ -56,10 +56,6 @@
       Condition=" (('$(ProjectTargetFrameworkIdentifier)' == '${DefaultNetCoreTargetFramework}') AND '${DefaultNetCoreTargetFramework}' == '$(ProjectTargetFrameworkVersion)') AND '$(TargetLatestDotNetRuntime)' != 'false' "
       RuntimeFrameworkVersion="${MicrosoftNETCoreAppRefVersion}"
       TargetingPackVersion="${MicrosoftNETCoreAppRefVersion}" />
-
-    <PackageReference Include="Microsoft.DotNet.ILCompiler"
-      Condition=" '$(PublishAot)' == 'true' "
-      Version="${MicrosoftNETCoreAppRefVersion}" />
   </ItemGroup>
 
   <ItemGroup>
@@ -118,6 +114,11 @@
           Condition=" '%(TargetFramework)' == '${DefaultNetCoreTargetFramework}' ">${MicrosoftNETCoreAppRefVersion}</ILLinkPackVersion>
     </KnownILLinkPack>
 
+    <KnownILCompilerPack Update="Microsoft.DotNet.ILCompiler">
+      <ILCompilerPackVersion
+        Condition="'%(TargetFramework)' == '${DefaultNetCoreTargetFramework}'">$(MicrosoftNETCoreAppRefVersion)</ILCompilerPackVersion>
+    </KnownILCompilerPack>
+
     <!-- Use the just-built ASP.NET Core shared framework if available except when building product code in servicing. -->
     <KnownFrameworkReference Update="Microsoft.AspNetCore.App" Condition=" $(UpdateAspNetCoreKnownFramework) ">
       <LatestRuntimeFrameworkVersion