Implement `follow-tooltip' on NS as well

Implement `follow-tooltip' on NS as well

* lisp/term/ns-win.el (x-begin-drag): Pass `follow-tooltip'.
* src/nsfns.m (Fx_show_tip): Record last dx and dy.
(syms_of_nsfns): New staticpros.
* src/nsmenu.m ([EmacsTooltip moveTo:]): New method.

* src/nsselect.m (Fns_begin_drag): New parameter
`follow-tooltip'.

* src/nsterm.h (@interface EmacsWindow):
(EmacsTooltip): Update prototypes.
* src/nsterm.m ([EmacsWindow draggedImage:movedTo:]): Move any
tooltip to the right location.
([EmacsWindow beginDrag:forPasteboard...]): New parameter
`followTooltip'.