Rename system tooltip variables to `use-system-tooltips'

Rename system tooltip variables to `use-system-tooltips'

* doc/emacs/frames.texi (Tooltips):
* doc/emacs/haiku.texi (Haiku Basics):
* doc/lispref/display.texi (Tooltips): Document
`use-system-tooltips' instead.

* etc/NEWS: Announce new option.
* lisp/cus-start.el (standard): Add new option.

* lisp/term/haiku-win.el (haiku-use-system-tooltips):
* lisp/term/pgtk-win.el (x-gtk-use-system-tooltips):
* lisp/term/x-win.el (x-gtk-use-system-tooltips): Add aliases
for old options.

* src/frame.c (syms_of_frame): New variable
`use-system-tooltips'.

* src/haikufns.c (Fx_show_tip):
(syms_of_haikufns):
* src/pgtkfns.c (x_hide_tip):
(Fx_show_tip):
(syms_of_pgtkfns):
* src/xfns.c (x_hide_tip):
(Fx_show_tip):
(syms_of_xfns): Use `use-system-tooltips' instead of the old
platform dependent options.