RSRP-210291: Smart completion in WPF

<UserControl x:Class="JetBrains.ReSharper.Features.Environment.src.Options.Inspections.InspectionSeverityTree"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:TreeListView="clr-namespace:JetBrains.UI.Avalon.TreeListView;assembly=JetBrains.Platform.ReSharper.UI"
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <TreeListView:TreeListView>
            <TreeListView:TreeListView.Columns>
                {caret}
            </TreeListView:TreeListView.Columns>
        </TreeListView:TreeListView>
    </Grid>
</UserControl>