Add control rendering tests with enabled visual styles

[RussKie]

We have a number of rendering tests, however all of them have been developed for disabled visual styles.
New tests need to be added to:

• NumericUpDownTests (https://github.com/dotnet/winforms/blob/master/src/System.Windows.Forms/tests/UnitTests/NumericUpDownTests.cs)
• ButtonRenderingTests (https://github.com/dotnet/winforms/blob/master/src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ButtonRenderingTests.cs)

Relates to #4197