Diagnostic that spans across projects

I'd like to implement a diagnostic analyzer that spans across `Project`s in a `Solution`. Is it possible to get this information within a diagnostic analyzer?

For reference, this is part of implementing the following:
https://github.com/openstacknetsdk/OpenStackNetAnalyzers/issues/16
