Rework the Destination filesystem to make --renderStaticToDisk work

See #9626

hugofs/decorators.go

@@ -23,6 +23,10 @@ import (
 	"github.com/spf13/afero"
 )
 
+var (
+	_ FilesystemUnwrapper = (*baseFileDecoratorFs)(nil)
+)
+
 func decorateDirs(fs afero.Fs, meta *FileMeta) afero.Fs {
 	ffs := &baseFileDecoratorFs{Fs: fs}
 
@@ -151,6 +155,10 @@ type baseFileDecoratorFs struct {
 	decorate func(fi os.FileInfo, filename string) (os.FileInfo, error)
 }
 
+func (fs *baseFileDecoratorFs) UnwrapFilesystem() afero.Fs {
+	return fs.Fs
+}
+
 func (fs *baseFileDecoratorFs) Stat(name string) (os.FileInfo, error) {
 	fi, err := fs.Fs.Stat(name)
 	if err != nil {