feat(debuginfo): Expose inline functions from PDBs

[jan-auer]

This PR resolves inline sites and exposes them as inline functions via the unified interface. SymCaches are then able to resolve inline frames.

Seems like we're taking a few more iterations to nail the final public interface in the pdb crate. Until the last PR is merged and the crate released, this will require the develop branch in my fork. This will block releases on crates.io, unfortunately.

For a description of the underlying structures in PDBs, see:

• Add support for inlinee lines pdb#47 (Inline sites and lines)
• Implement support for IPI types pdb#51 (IPI types for function names)
• Implement Cross Module Imports pdb#54 (Cross module imports)