Optionally reuse tooltip frames instead of deleting/recreating them.

Optionally reuse tooltip frames instead of deleting/recreating them.

* src/frame.c (tooltip_reuse_hidden_frame): New option.
* src/w32fns.c (x_create_tip_frame): Remove argument TEXT.  Fix
handling of dividers.
(x_hide_tip): New function.
(Fx_show_tip): Try to reuse old tooltip frame when
`tooltip-reuse-hidden-frame' is non-nil and frame parameters
have not changed.  Insert STRING here instead of passing it to
x_create_tip_frame.  Compute size of tooltip window with
Fwindow_text_pixel_size.  Obey Vw32_tooltip_extra_pixels when
padding tooltip window.
(Fx_hide_tip): Call x_hide_tip.
(Vw32_tooltip_extra_pixels): New variable.
* src/xdisp.c (Fwindow_text_pixel_size): Don't return negative y
value.  Fix doc-string.
* src/xfns.c (x_create_tip_frame): Remove argument TEXT.  Call
make_frame with mini_p argument false.
(x_hide_tip): New function.
(Fx_show_tip): Try to reuse old tooltip frame when
`tooltip-reuse-hidden-frame' is non-nil and frame parameters
have not changed.  Insert STRING here instead of passing it to
x_create_tip_frame.  Compute size of tooltip window with
Fwindow_text_pixel_size.
(Fx_hide_tip): Call x_hide_tip.
* lisp/cus-start.el (tooltip-reuse-hidden-frame): Add
customization entry.