When making a readable page in EWW, include the <title> and similar tags

When making a readable page in EWW, include the <title> and similar tags

* lisp/net/eww.el (eww--walk-readability, eww-readable-dom): New
functions.
(eww-display-html): Call 'eww-readable-dom'.
(eww-readable): Call 'eww-readable-dom'.  Don't copy over 'eww-data'
properties that our new readable page can handle on its own.
(eww-score-readability): Rewrite in terms of 'eww--walk-readability'.
Make obsolete.
(eww-highest-readability): Make obsolete.

* test/lisp/net/eww-tests.el (eww-test--lots-of-words)
(eww-test--wordy-page): New variables...
(eww-test/readable/toggle-display): ... use them.
(eww-test/readable/default-readable): Make sure that the readable page
includes the <title> and <link> tags (bug#77299).

(cherry picked from commit 2bdcf0250acecdb0719203ae711aedf5baad1783)