This might make it easier for simple project scenarios, also making it easier to understand what files are used in which tests. Currently, this is a bit indirect via the test class name and the corresponding folder under Scenarios.

This is easier to visualize than the current ordering where they end up last.

Since the PrivateAssets attribute is not a good fit in this scenario (see NuGet/Home#6041), use the common Pack metadata attribute and default it to false for MSBuild dependencies by default for build package kind.

Fixes NuGet/Home#6041

When using `<PackageReference PrivateAssets=all `, transitive dependencies were not being brough in. This required package authors to reference explicitly each and every package they wanted packaged as private assets. This was particularly annoying for build and analyzer packages, which need to package all their dependencies privately.

This commit leverages the SDK-provided `RunResolvePackageDependencies` which returns the transitive closure of all referenced packages as a list of package>parent list. We use that to add the concept of "implicit package references" that basically share the PrivateAssets=all that brought them in. The inference target then just considers both `@(PackageReference)` as well as `@(ImplicitPackageReference)` to determine the primary output dependencies to pack, but otherwise the existing logic remains unchanged.

This behavior still honors the `Pack=false` on the PackageReference, but also skips the implificly defined packages like NETStandard.Library and Microsoft.NETCore.

Fixes NuGet/Home#5103.