Add support for Cargo's virtual workspaces

[gmathiou4]

Found 4 Cargo definition file(s) at:
       Cargo.toml
       common/Cargo.toml
       summarizer/Cargo.toml
       new-summarizer/Cargo.toml
Found in total 4 definition file(s) from the following 1 package manager(s):
        Cargo
[DefaultDispatcher-worker-1] ERROR org.ossreviewtoolkit.analyzer.PackageManager - Cargo failed to resolve dependencies for path 'Cargo.toml': IllegalArgumentException: Virtual workspaces are not supported.