gnu: emacs-xwidgets{,-next-pgtk}: Use webkitgtk-with-libsoup2.

* gnu/packages/emacs.scm (emacs-xwidgets, emacs-next-pgtk)[inputs]:
Replace webkitgtk with webkitgtk-with-libsoup2.
* gnu/packages/webkit.scm (webkitgtk-with-libsoup2): Add further
information about where this package is used and upstream tracker for
libsoup3.

gnu/packages/emacs.scm

@@ -354,7 +354,7 @@ languages.")
        `(("gsettings-desktop-schemas" ,gsettings-desktop-schemas)
          ("glib-networking" ,glib-networking)))
       (inputs
-       `(("webkitgtk" ,webkitgtk)
+       `(("webkitgtk" ,webkitgtk-with-libsoup2)
          ,@(package-inputs emacs-next)))
       (home-page "https://github.com/masm11/emacs")
       (synopsis "Emacs text editor with @code{pgtk} and @code{xwidgets} support")
@@ -400,7 +400,7 @@ editor (with xwidgets support)")
            (delete 'restore-emacs-pdmp)
            (delete 'strip-double-wrap)))))
     (inputs
-     `(("webkitgtk" ,webkitgtk)
+     `(("webkitgtk" ,webkitgtk-with-libsoup2)
        ("libxcomposite" ,libxcomposite)
        ,@(package-inputs emacs)))))
 

gnu/packages/webkit.scm

@@ -364,6 +364,9 @@ HTML/CSS applications to full-fledged web browsers.")
 
 ;;; Required by gnome-online-accounts; as webkitgtk 2.34 propagates libsoup 3,
 ;;; which causes the build to fail.
+;;; Also required by e.g. emacs-next-pgtk,  emacs-xwidgets, and some other
+;;; Gnome packages for webkit2gtk-4.0. See also the upstream tracker for
+;;; libsoup 3: https://gitlab.gnome.org/GNOME/libsoup/-/issues/218
 (define-public webkitgtk-with-libsoup2
   (package/inherit webkitgtk
     (name "webkitgtk-with-libsoup2")