Drop references to the GNOME wiki from the docs

The GNOME wiki is getting decommissioned and archived:

  https://gitlab.gnome.org/Teams/Websites/General/-/issues/311

While the pages will still exist, it's better to direct people to
locations that are actively maintained.

CONTRIBUTING.md

@@ -100,14 +100,16 @@ development tools appropriate for your operating system, including:
  - Meson
  - Ninja
  - Gettext (19.7 or newer)
- - a [C99 compatible compiler](https://wiki.gnome.org/Projects/GLib/CompilerRequirements)
+ - a [C99 compatible compiler][glib-toolchain-reqs]
 
 Up-to-date instructions about developing GNOME applications and libraries
 can be found on [the GNOME Developer Center](https://developer.gnome.org).
 
 The GTK project uses GitLab for code hosting and for tracking issues. More
-information about using GitLab can be found [on the GNOME
-wiki](https://wiki.gnome.org/GitLab).
+information about using GitLab can be found on [the GNOME handbook][handbook].
+
+[glib-toolchain-reqs]: https://gitlab.gnome.org/GNOME/glib/-/blob/main/docs/toolchain-requirements.md
+[handbook]: https://handbook.gnome.org/infrastructure/gitlab.html
 
 ### Dependencies
 
@@ -131,7 +133,7 @@ GTK will attempt to download and build some of these dependencies if it
 cannot find them on your system.
 
 Additionally, you may want to look at projects that create a development
-environment for you, like [jhbuild](https://wiki.gnome.org/HowDoI/Jhbuild)
+environment for you, like [jhbuild](https://gitlab.gnome.org/GNOME/jhbuild)
 and [gvsbuild](https://github.com/wingtk/gvsbuild).
 
 ### Getting started

README.md

@@ -39,18 +39,21 @@ Nightly documentation can be found at
   - Gsk: https://gnome.pages.gitlab.gnome.org/gtk/gsk4/
 
 Nightly flatpaks of our demos can be installed from the
-[GNOME Nightly](https://wiki.gnome.org/Apps/Nightly) repository:
-  - `flatpak remote-add --if-not-exists gnome-nightly https://nightly.gnome.org/gnome-nightly.flatpakrepo`
-  - `flatpak install gnome-nightly org.gtk.Demo4`
-  - `flatpak install gnome-nightly org.gtk.WidgetFactory4`
-  - `flatpak install gnome-nightly org.gtk.IconBrowser4`
+[GNOME Nightly](https://nightly.gnome.org/) repository:
+
+```sh
+flatpak remote-add --if-not-exists gnome-nightly https://nightly.gnome.org/gnome-nightly.flatpakrepo
+flatpak install gnome-nightly org.gtk.Demo4
+flatpak install gnome-nightly org.gtk.WidgetFactory4
+flatpak install gnome-nightly org.gtk.IconBrowser4
+```
 
 Building and installing
 -----------------------
 
 In order to build GTK you will need:
 
-  - [a C99 compatible compiler](https://wiki.gnome.org/Projects/GLib/CompilerRequirements)
+  - [a C99 compatible compiler](https://gitlab.gnome.org/GNOME/glib/-/blob/main/docs/toolchain-requirements.md)
   - [Python 3](https://www.python.org/)
   - [Meson](http://mesonbuild.com)
   - [Ninja](https://ninja-build.org)

docs/reference/gtk/building.md

@@ -140,7 +140,7 @@ Other libraries are maintained separately.
   file formats. It is available [here](ttps://download.gnome.org/sources/gdk-pixbuf/).
 - [Pango](http://www.pango.org) is a library for internationalized
   text handling. It is available [here](https://download.gnome.org/sources/pango/).
-- [GObject Introspection](https://wiki.gnome.org/Projects/GObjectIntrospection)
+- [GObject Introspection](https://gitlab.gnome.org/GNOME/gobject-introspection)
   is a framework for making introspection data available to language
   bindings. It is available [here](https://download.gnome.org/sources/gobject-introspection/).
 - The [GNU libiconv](https://www.gnu.org/software/libiconv/) library

docs/reference/gtk/getting_started.md

@@ -245,9 +245,6 @@ to connect the "clicked" signal with [method@Gtk.Window.destroy], then the funct
 would be called on `button` (which would not go well, since the function expects
 a `GtkWindow` as argument).
 
-More information about creating buttons can be found
-[here](https://wiki.gnome.org/HowDoI/Buttons).
-
 The rest of the code in `example-1.c` is identical to `example-0.c`. The next
 section will elaborate further on how to add several [class@Gtk.Widget]s to your
 GTK application.

docs/reference/gtk/osx.md

@@ -7,5 +7,5 @@ on top of the Quartz API.
 Currently, the macOS port does not use any additional commandline options
 or environment variables.
 
-For up-to-date information about the current status of this port, see the
-[project page](https://wiki.gnome.org/Projects/GTK/OSX).
+For up-to-date information on building, installation, and bundling, see the
+[GTK website](https://www.gtk.org/docs/installations/macos).

gtk/gtkapplication.c

@@ -108,8 +108,8 @@
  *
  * ## See Also
  *
- * [HowDoI: Using GtkApplication](https://wiki.gnome.org/HowDoI/GtkApplication),
- * [Getting Started with GTK: Basics](getting_started.html#basics)
+ * - [Using GtkApplication](https://developer.gnome.org/documentation/tutorials/application.html)
+ * - [Getting Started with GTK: Basics](getting_started.html#basics)
  */
 
 enum {

gtk/gtkmenutracker.c

@@ -44,7 +44,7 @@
  *
  * Certain properties on the GtkMenuTrackerItem are mutable, and you must
  * listen for changes in the item. For more details, see the documentation
- * for GtkMenuTrackerItem along with https://wiki.gnome.org/Projects/GLib/GApplication/GMenuModel.
+ * for GtkMenuTrackerItem along with GMenuModel's reference.
  *
  * The idea of @with_separators is for special cases where menu models may
  * be tracked in places where separators are not available, like in toplevel