Make NS port use the normal dnd functions.

Make NS port use the normal dnd functions.

* lisp/term/ns-win.el: Require dnd.
(global-map): Remove drag items.
(ns-insert-text, ns-set-foreground-at-mouse)
(ns-set-background-at-mouse): Remove
(ns-drag-n-drop, ns-drag-n-drop-other-frame)
(ns-drag-n-drop-as-text, ns-drag-n-drop-as-text-other-frame): New
functions.

* src/nsterm.h (KEY_NS_DRAG_FILE, KEY_NS_DRAG_COLOR, KEY_NS_DRAG_TEXT):
Remove.

* src/nsterm.m (Qfile, Qurl): New.
(EV_MODIFIERS2): New macro.
(EV_MODIFIERS): Use EV_MODIFIERS2.
(ns_term_init): Remove font and color from DND, does not work on
newer OSX, and other ports don't have them.
(performDragOperation:): Handle modifiers used during drag.
Use DRAG_N_DROP_EVENT instead of NS specific events.
Remove global Lisp variables used to communicate with ns-win.el.
Remove font and color handling.
(syms_of_nsterm): Defsym Qfile and Qurl.

Fixes: debbugs:8051