Document new application bootstrap and analyzers

* [x] Document the current state of [Windows Forms application configuration and bootstrap design](https://github.com/dotnet/designs/blob/main/accepted/2021/winforms/streamline-application-bootstrap.md) as implemented in [dotnet/winforms#5035](https://github.com/dotnet/winforms/pull/5035).
* [x] Document the analyzers
* [x] Document the VS Designer support (❔)