Adapt doc-view-set-slice-using-mouse to touch-screen input

Adapt doc-view-set-slice-using-mouse to touch-screen input

* doc/lispref/commands.texi (Touchscreen Events): Document means
of unconditionally enabling simple conversion.

* lisp/doc-view.el (doc-view-set-slice-using-mouse): Bind
touch-screen-simple-mouse-conversion to t, and read translated
mouse events with read-key rather than read-event.

* lisp/subr.el (read-key): Don't permit idle timer to interfere
with reporting of translated mouse events.

* lisp/touch-screen.el (touch-screen-simple-mouse-conversion):
New variable.
(touch-screen-handle-point-up, touch-screen-handle-touch):
Unconditionally enable `mouse-drag' translation if set.  Decide
whether to send drag or mouse events by the values of the two
touchpoints' XY positions and point and double-click-fuzz, as in
make_lispy_event.

(cherry picked from commit 65bd41d1cf6d8ea6b95b69d9c60b0111a1c33392)