Adapt eww to touch screens, mice and text conversion

Adapt eww to touch screens, mice and text conversion

* doc/emacs/input.texi (On-Screen Keyboards): Update conditions
for displaying the virtual keyboard when t-s-d-k is enabled.

* etc/NEWS (Announce): Document changes.

* lisp/net/eww.el (eww-check-text-conversion): New function.
(eww-mode): Install it as a local post-command-hook.
(eww-submit-map, eww-submit-file, eww-checkbox-map): Bind
suitable commands to mouse-2.
(eww-form-submit, eww-form-checkbox, eww-form-file)
(eww-tag-select): Disguise inserted forms as buttons, that touch
event translation may prefer their bindings to mouse-2 over
mouse-1.
(eww-form-text, eww-tag-textarea): Insert field properties as
well.
(eww-select-file, eww-toggle-checkbox, eww-submit): New argument
EVENT, to whose position point is set.

* lisp/touch-screen.el (touch-screen-handle-point-up): Trivial
adjustments to the criteria for selecting mouse commands and
displaying the on screen keyboard.

(cherry picked from commit 4c46066cb6b3a9c87fb29be8cbdd4d90312f7020)