docs: Add initial support for using gi-docgen for docs

The files here are copied from the docs-gtk-org
branch of gtk.

This adds gi-docgen to the CI Dockerfiles and ensures the new versions
(including the OS upgrades from the previous commit) are used during CI.

Helps: #3037

docs/reference/meson.build

@@ -53,6 +53,25 @@ if get_option('gtk_doc')
   endif
 endif
 
-subdir('gio')
-subdir('glib')
-subdir('gobject')
+# gi-docgen version
+if get_option('gtk_doc')
+  gidocgen_dep = dependency('gi-docgen', version: '>= 2023.1',
+                          fallback: ['gi-docgen', 'dummy_dep'],
+                          required: true)
+
+  toml_conf = configuration_data()
+  toml_conf.set('VERSION', meson.project_version())
+
+  gidocgen = find_program('gi-docgen', required: true)
+
+  gidocgen_common_args = [
+    '--quiet',
+    '--no-namespace-dir',
+    '--fatal-warnings',
+  ]
+
+  subdir('glib')
+  subdir('gmodule')
+  subdir('gobject')
+  subdir('gio')
+endif