gnu: Make webkitgtk-next the new webkitgtk.

As of version 2.42.0, the WebKit 6.0 typelib is considered stable.
With GNOME itself moving to GTK4 as time marches on, we should reflect
the fact that this is the preferred Webkit for future applications.

* gnu/packages/webkit.scm (webkitgtk-next): Remove variable.  Inline logic…
(webkitgtk): … here.  Move old value …
(webkitgtk-for-gtk3): … here.
(webkitgtk-with-libsoup2): Inherit from webkitgtk-for-gtk3.
* gnu/packages/geo.scm (gnome-maps): Adjust accordingly.
* gnu/packages/gnome.scm (gnome-initial-setup, sushi)
(cambalache, devhelp, devhelp-with-libsoup2, gnome-online-accounts)
(gnome-online-accounts-3.44, evolution-data-server, evolution-data-server-3.44)
(lollypop, evolution, gnome-boxes, geary, komikku): Likewise.
* gnu/packages/guile-xyz.scm (guile-gi, nomad): Likewise.
* gnu/packages/lisp-xyz.scm (sbcl-cl-webkit): Likewise.
* gnu/packages/mail.scm (balsa): Likewise.
* gnu/packages/mate.scm (atril): Likewise.
* gnu/packages/music.scm (ctrlr): Likewise.
* gnu/packages/rednotebook.scm (rednotebook): Likewise.
* gnu/packages/syndication.scm (gfeeds): Likewise.
* gnu/packages/telegram.scm (telegram-desktop): Likewise.
* gnu/packages/vnc.scm (remmina): Likewise.
* gnu/packages/web-browsers.scm (nyxt): Likewise.

gnu/packages/guile-xyz.scm

@@ -3350,7 +3350,7 @@ list of components.  This module takes care of that for you.")
                   (guix build utils)
                   (ice-9 popen)
                   (ice-9 rdelim))
-       #:disallowed-references ,(list gtk+ webkitgtk)
+       #:disallowed-references ,(list gtk+ webkitgtk-for-gtk3)
        #:phases
        (modify-phases %standard-phases
          (add-after 'unpack 'remove-dotted-circle-from-combining-character
@@ -3396,7 +3396,7 @@ list of components.  This module takes care of that for you.")
     (propagated-inputs (list gobject-introspection))
     (inputs (list guile-3.0 glib
                   ;; For tests, only relevant when compiling natively
-                  gtk+ webkitgtk))
+                  gtk+ webkitgtk-for-gtk3))
     (home-page "https://github.com/spk121/guile-gi")
     (synopsis "GObject bindings for Guile")
     (description
@@ -3935,7 +3935,7 @@ processing filters.")
        ("glib-networking" ,glib-networking)
        ("gtk+" ,gtk+)
        ("gtk+:bin" ,gtk+ "bin")
-       ("webkitgtk" ,webkitgtk)
+       ("webkitgtk" ,webkitgtk-for-gtk3)
        ("gtksourceview" ,gtksourceview-4)
        ("gsettings-desktop-schemas" ,gsettings-desktop-schemas)
        ("vte" ,vte)