hugofs: Make FileMeta a struct

This commit started out investigating a `concurrent map read write` issue, ending by replacing the map with a struct.

This is easier to reason about, and it's more effective:

```
name                                  old time/op    new time/op    delta
SiteNew/Regular_Deep_content_tree-16    71.5ms ± 3%    69.4ms ± 5%    ~     (p=0.200 n=4+4)

name                                  old alloc/op   new alloc/op   delta
SiteNew/Regular_Deep_content_tree-16    29.7MB ± 0%    27.9MB ± 0%  -5.82%  (p=0.029 n=4+4)

name                                  old allocs/op  new allocs/op  delta
SiteNew/Regular_Deep_content_tree-16      313k ± 0%      303k ± 0%  -3.35%  (p=0.029 n=4+4)
```

See #8749

1 files changed, 14 insertions, 14 deletions

diff --git a/hugofs/walk.go b/hugofs/walk.go
index a46b36e50..44d58f060 100644
--- a/hugofs/walk.go
+++ b/hugofs/walk.go
@@ -73,7 +73,7 @@ type WalkwayConfig struct {
 func NewWalkway(cfg WalkwayConfig) *Walkway {
 	var fs afero.Fs
 	if cfg.Info != nil {
-		fs = cfg.Info.Meta().Fs()
+		fs = cfg.Info.Meta().Fs
 	} else {
 		fs = cfg.Fs
 	}
@@ -184,7 +184,7 @@ func (w *Walkway) walk(path string, info FileMetaInfo, dirEntries []FileMetaInfo
 	}
 
 	meta := info.Meta()
-	filename := meta.Filename()
+	filename := meta.Filename
 
 	if dirEntries == nil {
 		f, err := w.fs.Open(path)
@@ -206,7 +206,7 @@ func (w *Walkway) walk(path string, info FileMetaInfo, dirEntries []FileMetaInfo
 
 		dirEntries = fileInfosToFileMetaInfos(fis)
 
-		if !meta.IsOrdered() {
+		if !meta.IsOrdered {
 			sort.Slice(dirEntries, func(i, j int) bool {
 				fii := dirEntries[i]
 				fij := dirEntries[j]
@@ -214,7 +214,7 @@ func (w *Walkway) walk(path string, info FileMetaInfo, dirEntries []FileMetaInfo
 				fim, fjm := fii.Meta(), fij.Meta()
 
 				// Pull bundle headers to the top.
-				ficlass, fjclass := fim.Classifier(), fjm.Classifier()
+				ficlass, fjclass := fim.Classifier, fjm.Classifier
 				if ficlass != fjclass {
 					return ficlass < fjclass
 				}
@@ -222,20 +222,20 @@ func (w *Walkway) walk(path string, info FileMetaInfo, dirEntries []FileMetaInfo
 				// With multiple content dirs with different languages,
 				// there can be duplicate files, and a weight will be added
 				// to the closest one.
-				fiw, fjw := fim.Weight(), fjm.Weight()
+				fiw, fjw := fim.Weight, fjm.Weight
 				if fiw != fjw {
 					return fiw > fjw
 				}
 
 				// Explicit order set.
-				fio, fjo := fim.Ordinal(), fjm.Ordinal()
+				fio, fjo := fim.Ordinal, fjm.Ordinal
 				if fio != fjo {
 					return fio < fjo
 				}
 
 				// When we walk into a symlink, we keep the reference to
 				// the original name.
-				fin, fjn := fim.Name(), fjm.Name()
+				fin, fjn := fim.Name, fjm.Name
 				if fin != "" && fjn != "" {
 					return fin < fjn
 				}
@@ -252,7 +252,7 @@ func (w *Walkway) walk(path string, info FileMetaInfo, dirEntries []FileMetaInfo
 		meta := fim.Meta()
 
 		// Note that we use the original Name even if it's a symlink.
-		name := meta.Name()
+		name := meta.Name
 		if name == "" {
 			name = fim.Name()
 		}
@@ -267,13 +267,13 @@ func (w *Walkway) walk(path string, info FileMetaInfo, dirEntries []FileMetaInfo
 			pathMeta = strings.TrimPrefix(pathn, w.basePath)
 		}
 
-		meta[metaKeyPath] = normalizeFilename(pathMeta)
-		meta[metaKeyPathWalk] = pathn
+		meta.Path = normalizeFilename(pathMeta)
+		meta.PathWalk = pathn
 
-		if fim.IsDir() && w.isSeen(meta.Filename()) {
+		if fim.IsDir() && w.isSeen(meta.Filename) {
 			// Prevent infinite recursion
 			// Possible cyclic reference
-			meta[metaKeySkipDir] = true
+			meta.SkipDir = true
 		}
 	}
 
@@ -291,11 +291,11 @@ func (w *Walkway) walk(path string, info FileMetaInfo, dirEntries []FileMetaInfo
 		fim := fi.(FileMetaInfo)
 		meta := fim.Meta()
 
-		if meta.SkipDir() {
+		if meta.SkipDir {
 			continue
 		}
 
-		err := w.walk(meta.GetString(metaKeyPathWalk), fim, nil, walkFn)
+		err := w.walk(meta.PathWalk, fim, nil, walkFn)
 		if err != nil {
 			if !fi.IsDir() || err != filepath.SkipDir {
 				return err