* lisp/gnus/gnus-art.el: Add `event` args and operate at its position.

* lisp/gnus/gnus-art.el: Add `event` args and operate at its position.

(gnus-mime-save-part-and-strip)
(gnus-mime-delete-part, gnus-mime-save-part, gnus-mime-pipe-part)
(gnus-mime-view-part, gnus-mime-view-part-as-type)
(gnus-mime-copy-part, gnus-mime-print-part, gnus-mime-inline-part)
(gnus-mime-view-part-as-charset, gnus-mime-view-part-externally)
(gnus-mime-view-part-internally, gnus-article-press-button):
Add `event` arg and operate at its position.