Fix WinUI resource loading so if users replace resource keys in the platform App.Xaml file those will take precedence

Create a new .NET MAUI App

Add the following resource to the WinUI Head
```XAML

<Setter Property="Background" Value="Transparent" />
<Setter Property="Foreground" Value="{ThemeResource SystemControlForegroundBaseHighBrush}" />
<Setter Property="TabNavigation" Value="Local" />
<Setter Property="IsHoldingEnabled" Value="True" />
<Setter Property="Padding" Value="0, 0, 0, 0" />
<Setter Property="HorizontalContentAlignment" Value="Stretch" />
<Setter Property="VerticalContentAlignment" Value="Center" />
<Setter Property="MinWidth" Value="{ThemeResource ListViewItemMinWidth}" />
<Setter Property="MinHeight" Value="0" />



```

Now when you run the application you will get a crash because the `DefaultListViewItemStyle` is part of the WinUI Resources which are inserted after this style

The report identifies the WinUI Head resource declaration and the DefaultListViewItemStyle lookup; start by tracing where WinUI resources are inserted relative to MauiWinUIApplication.Resources. Reproduce the crash in a new .NET MAUI app with the shown XAML, then verify that an App.Xaml resource-key replacement takes precedence without crashing.

Written by the indexing model from the issue text.