Import ELPA package adaptive-wrap as visual-wrap

Import ELPA package adaptive-wrap as visual-wrap

* doc/emacs/basic.texi (Continuation Lines): Document
visual-wrap and its applications.

* etc/NEWS (Editing Changes in Emacs 30.1): Ditto.

* lisp/visual-wrap.el (visual-wrap-extra-indent)
(visual-wrap--face-extend-p, visual-wrap--prefix-face)
(visual-wrap--prefix, visual-wrap-fill-context-prefix)
(visual-wrap-prefix-function, visual-wrap-prefix-mode, lookup-key)
(visual-wrap): New file.  Update copyright years and rename to
`visual-wrap'.