Bug: Form Styling does not work for Mdi children

[wolframhaussig]

When having MDI children, only the parent form title is styled:

[wolframhaussig]

It seems that's a known bug in the .Net WinForms implementation:
https://www.github.com/dotnet/winforms/issues/3691

Our only option would be to handle the drawing ourselves. Starting point: https://www.pcreview.co.uk/threads/how-to-draw-custom-title-bars-on-mdi-child-forms.3200355/

If we want to do this, I guess this should be a StylableMdiChildForm and stored in our controls library.

[wolframhaussig]

Depends on the TabChild Control issue