[winforms] Document the Application type, specifically, the DoEvents object

[adegeo]

The Application type in WinForms isn't documented. DoEvents is a commonly used method to unblock the UI thread, however, it should be used careful and people frequently use it when there are better alternatives to choose from. DoEvents should be documented.

Reference articles:

• https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.application.doevents?view=windowsdesktop-7.0
• https://stackoverflow.com/questions/11352301/how-to-use-doevents-without-being-evil