Fix TreeView auto-expansion when opening trace files (#2218)

* Initial plan for issue

* Fix TreeView auto-expansion by binding IsExpanded property

Co-authored-by: brianrob <6210322+brianrob@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: brianrob <6210322+brianrob@users.noreply.github.com>

Author: Copilot

src/PerfView/MainWindow.xaml

@@ -198,6 +198,7 @@
                     <TreeView.ItemContainerStyle>
                         <Style TargetType="TreeViewItem">
                             <Setter Property="AutomationProperties.Name" Value="{Binding Name}" />
+                            <Setter Property="IsExpanded" Value="{Binding IsExpanded}" />
                         </Style>
                     </TreeView.ItemContainerStyle>
                     <TreeView.ItemTemplate>