Add utility functions and new xwidget commands

Add utility functions and new xwidget commands

Co-authored-by: Jaesup Kwak <veshboo@gmail.com>
* etc/NEWS: Announce new functions and options.
* lisp/xwidget.el (xwidget): New defgroup.
(xwidget-webkit-mode-map): Add new keybindings.
(xwidget-webkit-scroll-up, xwidget-webkit-scroll-down)
(xwidget-webkit-scroll-forward, xwidget-webkit-scroll-backward):
Add optional argument to specify specific amounts to scroll down.
(xwidget-webkit-scroll-up-line, xwidget-webkit-scroll-down-line): New
functions.
(xwidget-webkit-scroll-bottom): Fix function to scroll to the bottom
of the document.
(xwidget-webkit-callback): Use new function to update buffer title
even when Javascript is disabled.
(xwidget-webkit-bookmark-jump-new-session): New variable.
(xwidget-webkit-bookmark-make-record): Modify to use xwidget-webkit to
open bookmark that is created in xwidget-webkit.
(xwidget-webkit-insert-string): Fix Javascript snippet to not throw
Javsscript exceptions.
(xwidget-webkit-inside-pixel-width)
(xwidget-window-inside-pixel-height): New functions.
(xwidget-webkit-adjust-size-to-window): Use new functions.
(xwidget-webkit-new-session): Insert invisible URL instead of an empty
string to achieve better default behavior.
(xwidget-webkit-back, xwidget-webkit-forward, xwidget-webkit-reload)
(xwidget-webkit-current-url): Use new functions to enable scrolling
even when Javascript is disabled.
(xwidget-webkit-copy-selection-as-kill): Remove unnecessary lambda.
* src/nsxwidget.h src/nsxwidget.m (nsxwidget_webkit_uri)
(nsxwidget_webkit_title, nsxwidget_webkit_goto_history): Add new
functions.
* src/xwidget.c (Fxwidget_webkit_uri, Fxwidget_webkit_title)
(Fxwidget_webkit_goto_history): Add new functions.
(syms_of_xwidget): Define new functions.