extensions-app: Substitute gettext package in metainfo

The gettext domain name can be configured in meson options, but defaults
to 'gnome-shell' if it's built as a submodule.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3368>

subprojects/extensions-app/data/metainfo/meson.build

@@ -1,8 +1,12 @@
+metainfoconf = configuration_data()
+metainfoconf.set('app_id', app_id)
+metainfoconf.set('package_name', package_name)
+
 metainfo = i18n.merge_file(
   input: configure_file(
     input: base_id + '.metainfo.xml.in',
     output: app_id + '.metainfo.xml.in',
-    configuration: {'app_id': app_id},
+    configuration: metainfoconf,
   ),
   output: '@BASENAME@',
   po_dir: po_dir,

subprojects/extensions-app/data/metainfo/org.gnome.Extensions.metainfo.xml.in

@@ -21,7 +21,7 @@
     <name>The GNOME Project</name>
   </developer>
 
-  <translation type="gettext">gnome-extensions-app</translation>
+  <translation type="gettext">@package_name@</translation>
   <launchable type="desktop-id">@app_id@.desktop</launchable>
 
   <kudos>