bug#68072: pp functions have O(n^2) runtime with lisp-indent-function set to common-lisp-indent-function

[Brennan Vincent]

This also causes eglot (in its default configuration) to hang when
opening large Rust files, since rust-analyzer tends to send large amounts of
inlay hints, and eglot logs the messages it receives as pretty-printed
lisp objects.

Note the times in the comments here, showing clearly quadratic behavior:

(setq lisp-indent-function  'common-lisp-indent-function)

(defun bm1 (sz)
  (car
   (benchmark-run (progn (setq p (pp-to-string (make-list sz 'foo))) nil))))

(bm1 1000) ;; 0.057078079
(bm1 2000) ;; 0.22562238599999998
(bm1 10000) ;; 5.312058368
(bm1 20000) ;; 21.00088354