For the client library (`libSwiftDriver`), this is critical for multiplexing library instances, and for compatibility with different versions of `libSwiftDrvier`.
Resolves rdar://73631930
Adds a C API layer consisting of:
- Data structures used to represent in-memory result of dependency scanning
- Opaque dependency scanner tool (C wrapper for `DependencyScanningTool`)
Refactors `ScanDependencies.cpp` to produce dependency scanning result in the form of the above binary format.