Fix helperildll build race in Crossgen2 determinism test

[Copilot]

The determinism test rebuilt crossgen2smoke with a global OutputPath override, creating separate MSBuild instances that shared intermediate files. Concurrent writes to helperildll.dll could leave consumers reading incomplete metadata.

• Share the build: Replace the custom MSBuild invocation with a standard ProjectReference.
• Preserve the layout: Copy the three required DLLs into the determinism test’s existing input directory after building, without copying the smoke-test wrapper.

• Fixes Build race condition while building helperildll.dll #135717

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