RichTextBox/TextBox scrollbar is rendered incorrectly after changing DPI

[Olina-Zhang]

.NET version

.NET 11 RC2 build + integration/11.0-RC2 branch of Winforms repo

Did it work in .NET Framework?

Not tested/verified

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

NET11 new APIs

Issue description

When a WinForms application using VisualStylesMode.Net11, the RichTextBox vertical scrollbar is not rendered correctly after the DPI change.

The RichTextBox itself scales to the new DPI, but the vertical scrollbar does not appear to scale/layout consistently with the control.

100%DPI ->200%DPI:

200%DPI->100%DPI:

Steps to reproduce

1. Create a WinForms application targeting .NET 11.
2. Set VisualStylesMode = VisualStylesMode.Net11.
3. Add a RichTextBox and enter enough content to display the vertical scrollbar.
4. Set PerMonitorV2
5. Run the application, Move the application from one DPI to another DPI when DPI changed
6. Observe the RichTextBox vertical scrollbar after the DPI change.