Availability of `xwidget-webkit-load-html' on macOS

Hi all,

I'm not familiar with xwidget code, but is there a reason why
`xwidget-webkit-load-html' is missing on macOS?  I've compiled Emacs
with '--with-xwidgets' and it works:

  (featurep 'xwidget-internal) => t

But that function in xwidget.c is inside:

  #ifdef USE_GTK
  DEFUN ("xwidget-webkit-load-html", Fxwidget_webkit_load_html,
         Sxwidget_webkit_load_html, 2, 3, 0,
  ...

Same applies to `xwidget-webkit-back-forward-list'.  NEWS.29 doesn't say
anything about this as well.

Any hint?

Best, Arash

P.S. I also think the docstring of `make-xwidget' needs a polish.