* frame.c (x_redo_mouse_highlight): New function

* frame.c (x_redo_mouse_highlight): New function
to factor out common code used in W32 and X ports.
* dispextern.h (x_redo_mouse_highlight): Add prototype.
* xterm.h (struct x_display_info):
* w32term.h (struct w32_display_info):
* nsterm.h (struct ns_display_info): New members
last_mouse_motion_frame, last_mouse_motion_x and
last_mouse_motion_y, going to replace static variables below.
* xterm.c (last_mouse_motion_event, last_mouse_motion_frame)
(redo_mouse_highlight): Remove.
(note_mouse_movement, syms_of_xterm): Adjust user.
(handle_one_xevent): Likewise.  Use x_redo_mouse_highlight.
* w32term.c (last_mouse_motion_event, last_mouse_motion_frame)
(redo_mouse_highlight): Remove.
(note_mouse_movement, syms_of_w32term): Adjust user.
(w32_read_socket): Likewise.  Use x_redo_mouse_highlight.
* nsterm.m (last_mouse_motion_position, last_mouse_motion_frame):
Remove.
(note_mouse_movement, mouseMoved, syms_of_nsterm):
* nsfns.m (compute_tip_xy): Adjust user.