Opening a ContextMenu programmatically doesn't trigger the ContextMenuOpening event

- TargetFramework: net8.0-windows
- OS: Windows 11 Enterprise, x64
- Also reproducible on .NET Framework 4.8

# Problem Description

When a `ContextMenu` is opened programmatically by setting the `IsOpen` property to `true`, the `OnContextMenuOpening` handler is never called.

# Minimal repro

XAML:
```xaml

```

Code-behind
```cs
using System.Windows;
using System.Windows.Controls;

namespace WpfApp1
{
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}

protected override void OnContextMenuOpening(ContextMenuEventArgs e)
{
base.OnContextMenuOpening(e);
}

private void Button_Click(object sender, RoutedEventArgs e)
{
ctxMenu.IsOpen = true;
}
}
}
```

Clicking the button opens up the `ContextMenu` of the Window programmatically. Notice that the `OnContextMenuOpening` handler is never called.

# Expected behavior

The ContextMenu opens and the `OnContextMenuOpening` is called the same way it works when right-clicking to open it.

# Actual behavior

The ContextMenu opens but the `OnContextMenuOpening` method is never called.

# Regression?

I also tested on a project with the `.NET Framework 4.8` Target Framework and the issue is still reproducible.