Document obsoletion of 'intangible' and 'point-entered/left'

Document obsoletion of 'intangible' and 'point-entered/left'

* doc/lispref/text.texi (Special Properties): Document the new
properties 'cursor-intangible' and 'cursor-sensor-functions'.
Document the obsolete status of 'intangible', 'pointer-left',
and 'point-entered' properties, and of 'inhibit-point-motion-hooks'.
* doc/lispref/display.texi (Overlay Properties): Document that
'intangible' overlay property is obsolete.

* lisp/emacs-lisp/cursor-sensor.el (cursor-sensor-mode): Doc fix.