Update documentation for `System.Windows.Forms.Design` namespace and designer-related classes in `System.ComponentModel.Design` to indicate that .NET 3*/5/6 types are not compatible with the VS

[Tanya-Solyanik]

Theses classes are provided to applications that are implementing IDE functionality outside the VS, for example ability to show and edit controls on the design surface.

Currently users are implementing outdated samples, to support VisualStudio design time experience, like this one

See issue https://github.com/dotnet/winforms/issues/4239

[RussKie]

@Tanya-Solyanik I'm happy to help but I'm not exactly sure what the target state is.

[Tanya-Solyanik]

I would document the current state.

[merriemcgaw]

@Tanya-Solyanik Can you give a quick write up of what you'd like to see?

[merriemcgaw]

And would this be better moved to the docs repo?

[oudi]

outdated samples? Is there any other sample to support VisualStudio design time at .net core 3*/5/6？

[dreddy-work]

@Tanya-Solyanik / @RussKie / @merriemcgaw , what is the decision here. 7.0 milestone need to be closed.

[merriemcgaw]

Closing. We did do an update blog and @KlausLoeffelmann is getting samples and docs together.