A few changes required to enable the use of the native PDB reader when debugging minidumps:
- Consume PDBs even if the module binary is not available Implementing a PlaceholderObjectFile to complement the existing PlaceholderModule
- Use the minidump exception record if present
- Add support for "target symbols add" with PDBs
Overall this is a modest step towards improving the minidump debugging experience. But more importantly,
it enables the basic consumption of PDBs using the NativePDB(TM) reader as a foundation to add more functionality incrementally.