feat: support perspective name qualification

[DavePearce]

The exp benchmark uses perspectives, and also makes use of "perspective qualified names" of the form perspective/column. These need to be supported so this test can be enabled.

[DavePearce]

I think the pathway here is:

• Adjust Symbol so that it now has a Path.
• A Path can be relative or absolute (the latter being rooted in a particular module).
• Allow modules to be nested.
• Manage issue of looking up relative names (e.g. Path.Child() for example).
• Can we then remove the GlobalScope entirely I wonder?