Make build.writeStats a struct

So you can do

```toml
[build.writeStats]
  tags = true
  classes = true
  ids = false
```

Fixes #11191

publisher/publisher.go

@@ -81,8 +81,8 @@ func NewDestinationPublisher(rs *resources.Spec, outputFormats output.Formats, m
 	fs := rs.BaseFs.PublishFs
 	cfg := rs.Cfg
 	var classCollector *htmlElementsCollector
-	if rs.BuildConfig().WriteStats {
-		classCollector = newHTMLElementsCollector()
+	if rs.BuildConfig().WriteStats.Enabled() {
+		classCollector = newHTMLElementsCollector(rs.BuildConfig().WriteStats)
 	}
 	pub = DestinationPublisher{fs: fs, htmlElementsCollector: classCollector}
 	pub.min, err = minifiers.New(mediaTypes, outputFormats, cfg)