bug#48666: Leaks are still possible in hook--depth-alist

[jakanakaevangeli]

    (with-temp-buffer
      (add-hook 'post-command-hook (make-symbol "fun-sym") 77 t))
    (get 'post-command-hook 'hook--depth-alist)

Perhaps hook--depth-alist could be a hash table with weak keys.

Best regards.