DropDownButton ContetMenu placement is hardcoded.

[xlsupport]

Describe the bug

A DropDownButton will always show its flyout with ContextMenu.Placement="Bottom".

Expected WPF design would use a default of "Bottom" (via MetaData or Control Template) but allow a developer to set a different Placement on the ContextMenu in Content.

Cause: The (protected) OnClick event handler.

protected override void OnClick()
 {
     base.OnClick();

     if (_contextMenu is null)
     {
         return;
     }

     _contextMenu.SetCurrentValue(MinWidthProperty, ActualWidth);
     _contextMenu.SetCurrentValue(ContextMenu.PlacementTargetProperty, this);
     _contextMenu.SetCurrentValue(
         ContextMenu.PlacementProperty,
         System.Windows.Controls.Primitives.PlacementMode.Bottom
     );
     _contextMenu.SetCurrentValue(ContextMenu.IsOpenProperty, true);
 }

It's bad practice. Please improve.

To Reproduce

Example: A window with a single DropDownButton with VerticalAlignment=Bottom: Flyout appears outside the window. (Until Wpf.Core detects the monitor Edge and reposition it.)

Expected behavior

Respect the (optional) Placement in the ContextMenu.

<ui:DropDownButton>
    <ui:DropDownButton.Flyout>
        <ContextMenu Placement="Top">

Screenshots

No response

OS version

win11

.NET version

net 10

WPF-UI NuGet version

4.0.3

Additional context

No response