Forbid ref packs from getting bundled with produced packages

[oleksandr-didyk]

In the past we have encountered issues where a project would bundle a ref pack for one of its dependencies into the produced package. If a downstream repo would then run the library / text pack during the build, the bundled ref pack would get loaded in, failing the build.

Example - Nuget.ProjectModel 6.2.2 would be bundled with one of the Arcade's packages. SBRP contained a ref pack for this dependency, which would get included in the produced intermediate. runtime would then execute the package during the build, resulting in the ref pack getting loaded in, failing the build (see dotnet/source-build-reference-packages#673 (comment)).

We should add a check for this in Arcade's tooling, warning / failing if such a situation is encountered.

[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.