Currently, InitialSyncFileMover assumes all existing files are regular files or directories; if one is a symlink we get an invariant. We sometimes create a symlink to put the WiredTiger journal files on another device. This means we must support some of the files to delete containing a symlink at the top level of their path. We must preserve that symlink, so files with the same relative path from the sync source go into the symlink destination directory.