`dotnetup runtime install windowsdesktop` should also install the core runtime

## Summary

When installing the Windows Desktop runtime via `dotnetup runtime install windowsdesktop@`, the core .NET runtime should also be automatically installed, since the Windows Desktop runtime archive does not include it.

## Background

From PR #52649 discussion: https://github.com/dotnet/sdk/pull/52649#discussion_r2775786011

The Windows Desktop runtime zip does **not** include the core runtime within it, unlike the ASP.NET Core runtime zip which bundles the core runtime. This means that applications using the Windows Desktop runtime will fail to run if only the Windows Desktop runtime is installed without the core runtime.

Testing confirmed that a Windows Desktop app does not work without the core runtime installed.

## Proposed Solution

When `dotnetup runtime install windowsdesktop@` is executed, dotnetup should:
1. Install the Windows Desktop runtime
2. Automatically install the matching core .NET runtime (if not already present)

## Additional Investigation

While the ASP.NET Core zip currently bundles the core runtime, it's worth verifying whether older versions of the ASP.NET Core zip also include the core runtime. If there are any ASP.NET Core versions where the core runtime is not bundled, we may need to handle those cases as well.

## Related

- PR #52649 - Install runtime(s) with dotnetup
- Relates to validation in `ArchiveInstallationValidator.cs`