Fix display of minibuffer prompt in ido.el

Fix display of minibuffer prompt in ido.el

* lisp/minibuffer.el (minibuffer--message-overlay-pos): New
function.
(set-minibuffer-message): Use it to determine where to show the
overlay with the temporary message.
* lisp/ido.el (ido-exhibit): Revert "Render Ido suggestions using
an overlay"; this restores the original code which inserted the
match-status information into the minibuffer, instead of
displaying it in an overlay with an after-string.  Put the special
'minibuffer-message' text property at the beginning of the
inserted text.  (Bug#39379)

* etc/NEWS:
* doc/lispref/display.texi (Displaying Messages):
* doc/lispref/text.texi (Special Properties): Document the
'minibuffer-message' text property and its effect.