Better diagnostic logging in RAR when marking CopyLocal=false

Sometimes it is very difficult to understand why some transitive dependencies are copied to the output directory while others aren't.

It would greatly help to improve logging in this code: https://github.com/Microsoft/msbuild/blob/xplat/src/XMakeTasks/AssemblyDependency/Reference.cs#L1226-L1247

Specifically, we already list all source items in the log: https://github.com/Microsoft/msbuild/blob/xplat/src/XMakeTasks/AssemblyDependency/ResolveAssemblyReference.cs#L1645 It would be nice to also print their Private metadata if present.

This way we can know which one specified their Private=false and let to exclusion. Otherwise we have to double-check in the log elsewhere what the metadata was. It's possible but hard to use.