Fix handling of webkit xwidget bookmarks

Fix handling of webkit xwidget bookmarks

Make jumping to a bookmarked webkit xwidget in another window or
another frame show the xwidget only in that window or frame and
refactor new session code used by the bookmark code (bug#52856).
In addition, make xwidget-webkit-clone-* commands work.

* lisp/xwidget.el (xwidget-webkit-clone-and-split-below)
(xwidget-webkit-clone-and-split-right): Unbreak these functions by
passing just the URL to them, not the message displaying it.
(xwidget-webkit-bookmark-jump-new-session): Adjust doc string,
rephrasing and removing a customization suggestion that cannot
take effect.
(xwidget-webkit-bookmark-jump-handler): New autoloaded function.
(xwidget-webkit-bookmark-make-record): Use it.
(xwidget-webkit--create-new-session-buffer): New function
extracted from `xwidget-webkit-new-session'.
(xwidget-webkit-new-session): Use it.