widget-factory: Precompile the ui file

It doesn't make a huge amount of difference, unfortunately.
diff --git a/demos/widget-factory/widget-factory.gresource.xml b/demos/widget-factory/widget-factory.gresource.xml
index 2af832c..ed04d38 100644
--- a/demos/widget-factory/widget-factory.gresource.xml
+++ b/demos/widget-factory/widget-factory.gresource.xml
@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <gresources>
   <gresource prefix="/org/gtk/WidgetFactory4">
-    <file preprocess="xml-stripblanks">widget-factory.ui</file>
+    <file alias='widget-factory.ui'>widget-factory.uic</file>
   </gresource>
   <gresource prefix="/org/gtk/WidgetFactory4">
     <file>widget-factory.css</file>
diff --git a/demos/widget-factory/widget-factory.uic b/demos/widget-factory/widget-factory.uic
new file mode 100644
index 0000000..01687f0
--- /dev/null
+++ b/demos/widget-factory/widget-factory.uic
Binary files differ