[VMR] CheckForImplicitPackageReferenceOverrides eliminates all runtime packs in the event of duplicates in aspnetcore

[directhex]

aspnetcore specifies dependencies on every known/published runtime pack & crossgen, and also a dependency on the runtime pack specified by $(TargetRuntimeIdentifier). For example, that means a dependency exists for both Microsoft.NETCore.App.Runtime.linux-x64 and Microsoft.NETCore.App.Runtime.ubuntu.22.04-x64 when building on Ubuntu. The former dependency is found in the source-build prebuilts, with a 7.0ish version number, and the latter is found from the runtime build with an 8.0ish version number. These are deduplicated, and only the runtime build version is used.

https://github.com/dotnet/aspnetcore/blob/600eb9aa53c052ec7327e2399744215dbe493a89/eng/Dependencies.props#L97-L110

However, when building a build where runtime is emitting runtime packs with the same filename as the prebuilts, and aspnetcore is also targeting the same RID, then the runtime pack dependencies are duplicated entirely, and the prebuilt versions are ignored entirely. The CheckForImplicitPackageReferenceOverrides task seems to not only deduplicate the entries, but eliminate them both. Subsequently, the build fails when crossgen2 is not found (because no crossgen package has been restored)

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.