data: Rename appdata to metainfo

The appdata file/directory name is deprecated.

Also change the desktop component type to desktop-application. Same reason.

data/meson.build

@@ -28,14 +28,14 @@ endif
 
 appstream_file = i18n.merge_file(
   input: configure_file(
-    input: 'org.gnome.Loupe.appdata.xml.in.in',
-    output: 'org.gnome.Loupe.appdata.xml.in',
+    input: 'org.gnome.Loupe.metainfo.xml.in.in',
+    output: 'org.gnome.Loupe.metainfo.xml.in',
     configuration: conf,
   ),
-  output: '@0@.appdata.xml'.format(app_id),
+  output: '@0@.metainfo.xml'.format(app_id),
   po_dir: '../po',
   install: true,
-  install_dir: iv_datadir / 'appdata'
+  install_dir: iv_datadir / 'metainfo'
 )
 
 # appstream_util = find_program('appstream-util', required: false)

data/org.gnome.Loupe.metainfo.xml.in.in

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<component type="desktop">
+<component type="desktop-application">
   <id>@APP_ID@.desktop</id>
   <metadata_license>CC0-1.0</metadata_license>
   <project_license>GPL-3.0-or-later</project_license>

po/POTFILES

@@ -4,9 +4,9 @@ data/gtk/image_view.ui
 data/gtk/properties_view.ui
 data/gtk/window.ui
 data/org.gnome.Loupe.desktop.in
-data/org.gnome.Loupe.appdata.xml.in
+data/org.gnome.Loupe.metainfo.xml.in
 data/org.gnome.Loupe.gschema.xml
 src/widgets/image_view.rs
 src/widgets/properties_view.rs
 src/widgets/application.rs
-src/widgets/window.rs
+src/widgets/window.rs