Handle the Aliases compile item metadata for PackageReference

[nkolev92]

SDK side of NuGet/Home#4989.

Design at https://github.com/NuGet/Home/blob/dev/designs/PackageReference-Extern-Alias.md.

As part of LockFileItem for compile items, the SDK needs to pass through the aliases property to the compiler.

[wli3]

@nkolev92 when that needed? looks like there is not much work from SDK, is that true? Would you drive testing?

[nkolev92]

There's not much work yeah.

Whenever possible, 3.1.400 would be nice given we'd need to coordinate 4 changes.

I might take a stab if I have time.

[nkolev92]

Fixed by #11451