1. Rebase on new LibraryExporter
2. Update dependency name to "fx/<name>" for reference assembly
3. Update framework friendly name
4. Fix dependency message regression
5. Update tests
- Removed unused message types
- Removed intermediate ProjectInfo and ProjectState types
- Renamed Snapshot to ProjectSnapshot and ProjectSnapshot to ProjectContextSnapshot
- Exposed Project on ProjectContextCollection
- Removed AllDiagnostics message since it won't be used
- Renamed ProjectContextManager to ProjectManager
- Create project context snapshot in one pass
- Create project contexts lookup inline
- Consistent naming of payloads
