Restore Microsoft.DotNet.TemplateLocator NuGet packaging on main

[Copilot]

Microsoft.DotNet.TemplateLocator stopped producing a NuGet package after pack-related project settings were removed in a prior branch prep change. This PR ports the release/10.0.1xx fix to main so TemplateLocator package publication behavior is restored.

• Packability restored

  • Reintroduces IsPackable for the project.
  • Adds source-build guard to keep pack disabled during DotNetBuild pass 1 (avoids incomplete multi-TFM package outputs in that phase).

• Project-reference outputs restored in package

  • Reattaches CopyProjectReferencesToPackage to TargetsForTfmSpecificBuildOutput.
  • Restores packaging of managed ProjectReference copy-local outputs into BuildOutputInPackage.

• Representative project-file change

  <IsPackable>true</IsPackable>
  <IsPackable Condition="'$(DotNetBuild)' == 'true' and '$(DotNetBuildPass)' != '2'">false</IsPackable>
  <TargetsForTfmSpecificBuildOutput>
    $(TargetsForTfmSpecificBuildOutput);CopyProjectReferencesToPackage
  </TargetsForTfmSpecificBuildOutput>
  
  <Target Name="CopyProjectReferencesToPackage" DependsOnTargets="ResolveReferences">
    <ItemGroup>
      <BuildOutputInPackage Include="@(ReferenceCopyLocalPaths->WithMetadataValue('ReferenceSourceTarget', 'ProjectReference'))" />
    </ItemGroup>
  </Target>

[Copilot]

Pull request overview

Restores NuGet packaging behavior for Microsoft.DotNet.TemplateLocator on main after prior project settings changes stopped producing the package.

Changes:

• Re-enables packing via IsPackable, while disabling pack during DotNetBuild pass 1 to avoid incomplete multi-TFM outputs.
• Ensures project-reference copy-local outputs are included in the NuGet package by adding a TFM-specific packaging target.