* lisp/arc-mode.el: Rewrite displaying the summaries

* lisp/arc-mode.el: Rewrite displaying the summaries

Completely rewrite the code that displayes the summaries, so all
backends share the same code.

(archive--summarize-descs): New function.
(archive-arc-summarize, archive-lzh-summarize, archive-zip-summarize)
(archive-zoo-summarize, archive-rar-summarize, archive-7z-summarize)
(archive-ar-summarize): Use it.
(archive-hidden-columns): New custom.
(archive-alternate-hidden-columns): New const.
(archive-mode-map): Always enable `archive-alternate-display`.
(archive-alternate-display): Set `archive-hidden-columns`.
(archive-hideshow-column): New command.
(archive--fit, archive--fit2, archive--enabled-p): New aux functions.