schemas: Define default app grid arrangement

Specify the default app grid arrangement. This makes the app grid
more useful since the interesting apps are prioritised. It also
communicates that the app grid can be customised.

Fixes https://gitlab.gnome.org/GNOME/gnome-shell/issues/3122

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1700>

data/org.gnome.shell.gschema.xml.in

@@ -50,7 +50,7 @@
       </description>
     </key>
     <key name="favorite-apps" type="as">
-      <default>[ 'org.gnome.Epiphany.desktop', 'org.gnome.Geary.desktop', 'org.gnome.Calendar.desktop', 'org.gnome.Music.desktop', 'org.gnome.Photos.desktop', 'org.gnome.Nautilus.desktop', 'org.gnome.Software.desktop' ]</default>
+      <default>[ 'org.gnome.Epiphany.desktop', 'org.gnome.Calendar.desktop', 'org.gnome.Music.desktop', 'org.gnome.Nautilus.desktop', 'org.gnome.Software.desktop' ]</default>
       <summary>List of desktop file IDs for favorite applications</summary>
       <description>
         The applications corresponding to these identifiers
@@ -113,7 +113,31 @@
       </description>
     </key>
     <key name="app-picker-layout" type="aa{sv}">
-      <default>[]</default>
+      <default><![CDATA[
+        [{
+          'org.gnome.Geary.desktop': <{'position': <0>}>,
+          'org.gnome.Contacts.desktop': <{'position': <1>}>,
+          'org.gnome.Weather.desktop': <{'position': <2>}>,
+          'org.gnome.clocks.desktop': <{'position': <3>}>,
+          'org.gnome.Maps.desktop': <{'position': <4>}>,
+          'org.gnome.Books.desktop': <{'position': <5>}>,
+          'org.gnome.Photos.desktop': <{'position': <6>}>,
+          'org.gnome.Totem.desktop': <{'position': <7>}>,
+          'org.gnome.Calculator.desktop': <{'position': <8>}>,
+          'org.gnome.gedit.desktop': <{'position': <9>}>,
+          'simple-scan.desktop': <{'position': <10>}>,
+          'gnome-control-center.desktop': <{'position': <11>}>,
+          'gnome-system-monitor.desktop': <{'position': <12>}>,
+          'org.gnome.Boxes.desktop': <{'position': <13>}>,
+          'org.gnome.Terminal.desktop': <{'position': <14>}>,
+          'Utilities': <{'position': <15>}>,
+          'org.gnome.Characters.desktop': <{'position': <16>}>,
+          'yelp.desktop': <{'position': <17>}>,
+          'org.gnome.Screenshot.desktop': <{'position': <18>}>,
+          'org.gnome.Cheese.desktop': <{'position': <19>}>,
+          'org.gnome.font-viewer.desktop': <{'position': <20>}>
+        }]
+      ]]></default>
       <summary>Layout of the app picker</summary>
       <description>
         Layout of the app picker. Each entry in the array is a page. Pages are