Text box/block context menu text color not updated on theme change

Nobody has claimed this yet.

### Describe the bug

Text box/block context menu text color is not updated on theme change (I am setting the `(XamlRoot.Content as FrameworkElement).RequestedTheme` property). The background updates correctly, but not the text, leaving it impossible to read. Possibly an issue with CommandBarFlyout in general.

### Why is this important?

My app allows updating the theme while running. Everything else apart from this works. It worked in UWP.

### Steps to reproduce the bug

Use the following XAML and code behind. Run the app, right click in the text box to show the context menu once, then change the theme using the button, then right click in the text box again and observe the text color of the context menu has not updated. Can do the same with the selection context menu for the text block.

```XAML

````

```C#
using Microsoft.UI.Xaml;

namespace TestContextMenu {
public sealed partial class MainWindow : Window {
public MainWindow() {
InitializeComponent();
}
private void changeThemeButton_Click(object sender, RoutedEventArgs e) {
((FrameworkElement)rootElement.XamlRoot.Content).RequestedTheme = ((FrameworkElement)rootElement.XamlRoot.Content).RequestedTheme != ElementTheme.Dark ? ElementTheme.Dark : ElementTheme.Light;
}
}
}
```

### Actual behavior

_No response_

### Expected behavior

_No response_

### Screenshots

_No response_

### NuGet package version

2.3.1

### Windows version

Windows 11 (25H2): Build 26200

### Additional context

_No response_

Start with the supplied XAML reproduction and changeThemeButton_Click, then inspect CommandBarFlyout and context-menu theme handling. Run the example with WinUI 2.3.1 and verify that TextBox and TextBlock selection context-menu text colors update after switching RequestedTheme.

Written by the indexing model from the issue text.