Implement non-system tooltips on NS

Implement non-system tooltips on NS

* src/nsfns.m (unwind_create_frame): Return Lisp_Object like on
X.
(do_unwind_create_frame): New function.
(Fx_create_frame): Adjust accordingly.
(compute_tip_xy): Fix coding style.
(unwind_create_tip_frame, ns_create_tip_frame): New functions.
(x_hide_tip, Fx_show_tip, Fx_hide_tip): Create and hide actual
tooltip frames.
(syms_of_nsfns): New defvar `x-max-tooltip-size' and staticpros.

* src/nsterm.m (ns_set_window_size): Clean up coding style.
([EmacsWindow initWithEmacsFrame:]):
([EmacsWindow initWithEmacsFrame:fullscreen:screen:]): Handle
tooltip frames.