extensions-app: Fix app ID in .Devel metainfo

The ID is currently hard-coded to the non-development one, with
the result that the .Devel app effectively doesn't have any
metainfo.

Fix that by configuring the file with the correct ID.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3158>

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

@@ -1,6 +1,10 @@
 metainfo = app_id + '.metainfo.xml'
 i18n.merge_file(
-  input: base_id + '.metainfo.xml.in',
+  input: configure_file(
+    input: base_id + '.metainfo.xml.in',
+    output: app_id + '.metainfo.xml.in',
+    configuration: {'app_id': app_id},
+  ),
   output: metainfo,
   po_dir: po_dir,
   install: true,

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

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <component type="desktop-application">
-  <id>org.gnome.Extensions</id>
+  <id>@app_id@</id>
 
   <name>Extensions</name>
   <summary>Manage your GNOME Extensions</summary>
@@ -22,7 +22,7 @@
   </developer>
 
   <translation type="gettext">gnome-extensions-app</translation>
-  <launchable type="desktop-id">org.gnome.Extensions.desktop</launchable>
+  <launchable type="desktop-id">@app_id@.desktop</launchable>
 
   <kudos>
     <kudo>HiDpiIcon</kudo>