This fixes the restore issues as all sources will now appear as if they were originally part of the source file system.
The backend implementation has now been simplified so the backends only return names of entries with no path information. Most backends already do this, but the S3 backends did not, so this was fixed as well.
This also clears up the interfaces, so the backend does not know about the `ISourceProviderEntry`. All mapping is done by the `BackendSourceProvider`, making it simpler to support other backends as sources.
With this interface it is possible to wrap the current support for snapshots and USN and simplify the enumeration.
This makes a number of assumptions into fields such as `IsMetaEntry` and `IsRootEntry` that removes code that was checking for various properties.
This first commit has support for VSS and USN as well as "naked" files, keeping feature parity.
There is also an experimental support for loading a backend-as-a-source. The support for this is currently limited as the backends need to be extended to support a folder concept.
Kenneth Skovhede