Add support for MSBuild 15 item metadata attribute notation

[kzu]

If your projects use, say:

<PackageReference Include="Moq" Version="*" />

Which is totally valid MSBuild 15+ notation, the tool fails with:

Unhandled Exception: System.AggregateException: One or more errors occurred. ---> Microsoft.Build.Exceptions.InvalidProjectFileException: The attribute "Version" in element <PackageReference> is unrecognized.
   at Microsoft.Build.Shared.ProjectErrorUtilities.ThrowInvalidProject(String errorSubCategoryResourceName, IElementLocation elementLocation, String resourceName, Object[] args)

Most likely because it's referencing MSBuild 14 or prior.

Thanks!

[alexsorokoletov]

@kzu this should go into project system project https://github.com/dotnet/project-system most probably.
Updating dependencies to latest should fix all that automagically.

[kzu]

It's not a project system thing IMHO. The project system already supports that attribute-based notation in MSBuild 15+/VS2017+.