Add packaged trimmed-publish regression coverage for F# async execution #7533

Summary

The packaged F# async preservation path has focused manual regression coverage but no automated trimmed-publish smoke test. A future SDK target or package-layout change could remove preservation and let an async test finish without executing its body. Add a packaged-app regression test to catch that failure in CI.

Reproduction

At e4c4769f6d, _TUnitPreserveFSharpAsync depends on the SDK-private _ComputeManagedAssemblyToLink target and loads a linker descriptor next to the packaged targets file. PR #7526 records manual positive and negative controls, including a runtime-only FSharp.Core dependency with ExcludeAssets="compile"; its automated package tests do not exercise this trimmed execution path.

Proposal

Add a CI smoke test consuming the produced NuGet packages. Publish a trimmed, non-AOT app with FSharp.Core and verify that an F# async side effect executes and an async exception propagates. Include the runtime-only FSharp.Core case and assert that the descriptor is shipped beside the targets in both build and buildTransitive layouts. Keep a C# publish without FSharp.Core warning-free. Demonstrate that disabling preservation makes the execution assertion fail.

Environment

Manual validation in #7526 used .NET SDK 10.0.403, macOS arm64. FSharp.Core IL2040 resource warnings are tracked separately upstream.

Please add this automated coverage for the packaged trimming path.