fix: use flattened Html element

DocGen4/Output/Navbar.lean

@@ -29,7 +29,7 @@ partial def moduleListDir (h : Hierarchy) : HtmlM Html := do
   pure
     <details "class"="nav_sect" "data-path"={moduleLink}
       [if (←getCurrentName).any (h.getName.isPrefixOf ·) then #[("open", "")] else #[]]>
-      <summary><a "href"={← moduleNameToLink h.getName}>{h.getName.toString}</a></summary>
+      {Html.element "summary" true #[] #[<a "href"={← moduleNameToLink h.getName}>{h.getName.toString}</a>]}
       [dirNodes]
       [fileNodes]
     </details>

DocGen4/ToHtmlFormat.lean

@@ -33,9 +33,9 @@ def attributesToString (attrs : Array (String × String)) :String :=
 
 -- TODO: Termination proof
 partial def toStringAux : Html → String
-| element tag false attrs #[text s] => s!"<{tag}{attributesToString attrs}>{s}</{tag}>"
+| element tag false attrs #[text s] => s!"<{tag}{attributesToString attrs}>{s}</{tag}>\n"
-| element tag false attrs #[child] => s!"<{tag}{attributesToString attrs}>{child.toStringAux}</{tag}>"
+| element tag false attrs #[child] => s!"<{tag}{attributesToString attrs}>\n{child.toStringAux}</{tag}>\n"
-| element tag false attrs children => s!"<{tag}{attributesToString attrs}>{children.foldl (· ++ toStringAux ·) ""}</{tag}>"
+| element tag false attrs children => s!"<{tag}{attributesToString attrs}>\n{children.foldl (· ++ toStringAux ·) ""}</{tag}>\n"
 | element tag true attrs children => s!"<{tag}{attributesToString attrs}>{children.foldl (· ++ toStringAux ·) ""}</{tag}>"
 | text s => s