[TODO] Extract TU bounds data + semantics from .pdb

The `pdb` crate has a struct [`ModuleInfo`](https://docs.rs/pdb/latest/pdb/struct.ModuleInfo.html) that contains symbols, inlines, imports, and exports for any given source obj. These should be plumbed to Jeff's internal split database, and the imports/exports should be used to govern weak/strong linkage.