feat(fs): Implement loading HTML from http.FileSystem (#4053)

* Implement loading HTML from http.FileSystem

* Add OnlyHTMLFS test

* Move OnlyHTMLFS to internal and add test

internal/fs/fs.go

@@ -0,0 +1,22 @@
+package fs
+
+import (
+	"io/fs"
+	"net/http"
+)
+
+// FileSystem implements an [fs.FS].
+type FileSystem struct {
+	http.FileSystem
+}
+
+// Open passes `Open` to the upstream implementation and return an [fs.File].
+func (o FileSystem) Open(name string) (fs.File, error) {
+	f, err := o.FileSystem.Open(name)
+
+	if err != nil {
+		return nil, err
+	}
+
+	return fs.File(f), nil
+}