(mark_window_display_accurate): Set region_showing fields.

(mark_window_display_accurate): Set region_showing fields.
(redisplay_window): Update region_showing field.
(display_text_line): Set region_showing to t if will show one.

(mark_window_display_accurate): Set region_showing fields.
(redisplay_window): Update region_showing field.
(display_text_line): Set region_showing to t if will show one.

(redisplay, redisplay_window): Don't use the cursor-motion
special-case code if the region is or was highlighted.

(display_text_line): Pass those args,
describing the region if the mark is transient and active.

(display_menu_bar): Update FRAME_MENU_BAR_ITEMS here.