RichTextBox is not fully borderless with BorderStyle=None under VisualStylesMode.NET11 #15055

.NET version

.NET 11 RC2 build: 11.0.100-rc.2.26455.110

Did it work in .NET Framework?

Not tested/verified

Did it work in any of the earlier releases of .NET Core or .NET 5+?

Occurs after New APIs in .NET11

Issue description

When RichTextBox.BorderStyle is set to None and VisualStylesMode is configured as NET11, visible border strokes are still rendered along the top and left edges of the control.
This behavior differs from the Classic visual style implementation, where no border is rendered when BorderStyle=None.

Steps to reproduce

1. Create a RichTextBox.
2. Set BorderStyle = None.
3. Set VisualStylesMode = NET11.
4. Run the application and observe the control.

Actual Result
Thin border lines remain visible on the top and left sides of the RichTextBox.
Expected Result
No border should be rendered on any side of the RichTextBox when BorderStyle=None, matching the behavior of Classic mode.