Recommend `Properties` metadata on `ProjectReference` items

The MSBuild task has hardcoded support for this, if you set `Properties` on a `ProjectReference` the properties will get passed as global properties to the project being built:

https://github.com/dotnet/msbuild/blob/8636afcc4514b48a1a34c8051a00d953abe1318c/src/Tasks/MSBuild.cs#L517-L528

We should offer it in IntelliSense for discoverability.