Add file metadata to FileEntry

[gfs]

It might be interesting to some consumers what the stated permissions and other metadata is available about the file. For example, some files could unzip with chmod +x and be executable.

This requires first to see what common factors are shared between SharpZipLib extracted entries, and also LibObjectFile file entries. For LibObjectFile entries reading real filesystems this is particularly interesting. Deciding on a new schema for FileEntry - either a number of fields or a FileMetadata object.

This is a feature request related to Attack Surface Analyzer.