[XSG] resolve xRefs through listnodes (#32028)

x:Reference optimization for XSG wasn't able to walk up the tree when a
node is a ListNode

- fixes #31995

Author: StephaneDelcroix

src/Controls/src/SourceGen/KnownMarkups.cs

@@ -480,7 +480,10 @@ internal static bool ProvideValueForReferenceExtension(ElementNode markupNode, S
 				value = $"{namescope.namesInScope[name!].Name}";
 				return true;
 			}
-			node = node.Parent as ElementNode;
+			INode n = node;
+			while (n.Parent is ListNode ln)
+				n = ln.Parent;
+			node = n.Parent as ElementNode;
 		}
 
 		//TODO report diagnostic

src/Controls/tests/Xaml.UnitTests/Issues/Maui31995.xaml

@@ -0,0 +1,50 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Microsoft.Maui.Controls.Xaml.UnitTests.Issues.Maui31995"
+             Title="Maui31995"
+             x:Name="thisControl24">
+    <VerticalStackLayout BindableLayout.ItemsSource="{Binding ItemsSource, Source={x:Reference thisControl24}}">
+        <BindableLayout.ItemTemplate>
+            <DataTemplate>
+                <Grid>
+                    <Grid.Triggers>
+                        <DataTrigger TargetType="Grid" Binding="{Binding Selected}" Value="False">
+                            <Setter Property="VisualStateManager.VisualStateGroups">
+                                <VisualStateGroupList>
+                                    <VisualStateGroup Name="CommonStates">
+                                        <VisualState Name="Normal">
+                                            <VisualState.Setters>
+                                                <Setter Property="BackgroundColor" Value="{Binding BackgroundColor, Source={x:Reference thisControl24}}"/>
+                                            </VisualState.Setters>
+                                        </VisualState>
+                                        <VisualState Name="PointerOver">
+                                            <VisualState.Setters>
+                                                <Setter Property="BackgroundColor" Value="{Binding BackgroundColor, Source={x:Reference thisControl24}}"/>
+                                            </VisualState.Setters>
+                                        </VisualState>
+                                    </VisualStateGroup>
+                                </VisualStateGroupList>
+                            </Setter>
+                        </DataTrigger>
+                        <DataTrigger TargetType="Grid" Binding="{Binding Selected}" Value="True">
+                            <Setter Property="VisualStateManager.VisualStateGroups">
+                                <VisualStateGroupList>
+                                    <VisualStateGroup Name="CommonStates">
+                                        <VisualState Name="Normal">
+                                            <VisualState.Setters>
+                                                <Setter Property="BackgroundColor" Value="{Binding BackgroundColor, Source={x:Reference thisControl24}}"/>
+                                            </VisualState.Setters>
+                                        </VisualState>
+                                    </VisualStateGroup>
+                                </VisualStateGroupList>
+                            </Setter>
+                        </DataTrigger>
+                    </Grid.Triggers>
+                    <Label Text="{Binding .}" />
+
+                </Grid>
+            </DataTemplate>
+        </BindableLayout.ItemTemplate>
+    </VerticalStackLayout>
+</ContentPage>

src/Controls/tests/Xaml.UnitTests/Issues/Maui31995.xaml.cs

@@ -0,0 +1,19 @@
+using System;
+using System.Collections.Generic;
+namespace Microsoft.Maui.Controls.Xaml.UnitTests.Issues;
+#nullable enable
+
+public partial class Maui31995 : ContentPage
+{
+	public Maui31995() => InitializeComponent();
+
+	int count = 0;
+	public List<object> ItemsSource = new();  // Added.
+
+
+
+	private void OnCounterClicked(object? sender, EventArgs e)
+	{
+		count++;
+	}
+}