Rework the Destination filesystem to make --renderStaticToDisk work

See #9626

hugofs/createcounting_fs.go

@@ -33,10 +33,18 @@ type DuplicatesReporter interface {
 	ReportDuplicates() string
 }
 
+var (
+	_ FilesystemUnwrapper = (*createCountingFs)(nil)
+)
+
 func NewCreateCountingFs(fs afero.Fs) afero.Fs {
 	return &createCountingFs{Fs: fs, fileCount: make(map[string]int)}
 }
 
+func (fs *createCountingFs) UnwrapFilesystem() afero.Fs {
+	return fs.Fs
+}
+
 // ReportDuplicates reports filenames written more than once.
 func (c *createCountingFs) ReportDuplicates() string {
 	c.mu.Lock()