Convert ibuffer menus to easymenu

Convert ibuffer menus to easymenu

* lisp/ibuffer.el (ibuffer-mode-map): Move menu from here...
(ibuffer-mode-mark-menu, ibuffer-mode-view-menu): ...to here.
Convert to easymenu.
(ibuffer-mode--groups-menu-definition): New function.  Fix bug where
"Kill filter by group named" and "Yank last killed filter group
before" was overwritten and never shown in the menu.
(ibuffer-mode-groups-popup): Convert to easymenu.
(ibuffer-mode-operate-menu): Rename from 'ibuffer-mode-operate-map'
and update uses.  Convert to easymenu.
(ibuffer-mode-operate-map): Make into obsolete alias for above
renamed variable.