popover: Install emoji layout

In order to do that, an additional piece of state (layout switcher) was exposed to the event handlers, a separation between squeekboard-only and system layouts was introduced, along with a Translation structure to prevent mixing up strings.

tests/meson.build

@@ -58,6 +58,8 @@ foreach layout : [
     'no',
     'number',
     'se',
+    
+    'emoji',
 ]
     test(
         'test_layout_' + layout,