This patch completely reworks TextNode::compute_text_for_rendering(). It
removes the unnecessary usage of Utf8View to find spaces in a String.
Furthermore, it adds a couple fast return paths for common but trivial
cases such as empty, single-character and whitespace-less strings.
For the HTML spec bookmarks, around two thirds of all function calls
(which amounts to around 10'000) use the fast paths and thus avoid
allocating a StringBuilder just to build a copy of the already present
String.
054c742d17