Port StringList items
This prevents several Workbench demos from being converted back and forth.
<object class="GtkDropDown">
<property name="model">
<object class="GtkStringList">
<items>
<item>Center Widget</item>
<item>👁️</item>
<item>❤️</item>
<item>💼</item>
<item>🪑</item>
</items>
</object>
</property>
</object>
Results in "unsupported XML tag: "