vfs: add Unwrap to loggingFS

As a wrapping VFS implementation, it should implement Unwrap and return the
contained FS.

Author: jbowens

vfs/logging_fs.go

@@ -118,6 +118,10 @@ func (fs loggingFS) RemoveAll(name string) error {
 	return err
 }
 
+func (fs loggingFS) Unwrap() FS {
+	return fs.FS
+}
+
 type loggingFile struct {
 	File
 	name  string