Improve 'emacs-news-view-mode' menus and bindings

Improve 'emacs-news-view-mode' menus and bindings

* lisp/textmodes/emacs-news-mode.el (emacs-news-mode-map): Move
non-editing commands from here...
(emacs-news-common-map): ... to here.
(emacs-news-view-mode): Remove hard-coded 'special-mode' bindings.
(emacs-news-view-mode-map): Inherit from 'special-mode-map' and
'emacs-news-common-map' here instead.
(emacs-news-mode--menu-common-1): New defconst for menu items common to
'news-mode' and 'news-view-mode'.
(emacs-news-mode--menu-common-2): Second new defconst for common items.
(emacs-news-mode-menu): Use them.
(emacs-news-view-mode-menu): New menu, which omits the buffer editing
commands.

This builds on the fix for Bug#72080.