Create code-only MonoGame Forms tutorial

[vchelaru]

This topic should include:

• Initial setup (nuget, Init/Update/Draw, Root). high level and link to other docs
• Create initial controls like Button, TextBox, CheckBox, and Radio Buttons
  • Set Button Text
  • TextBox Placeholder
  • RadioButton Groups
• Show how to handle in these controls
  • Button.Click
• Show how to populate ListBox and ComboBox
  • Using Items
  • Templates
• Gamepad Support - give initial tutorial, link to full document
• Styling - give initial tutorial, link to full document
• MVVM/Binding - give initial tutorial, we need a full document

This requires the following new features:

1. Add Label code-only
2. Add StackPanel code-only
3. Add FrameworkElement Root support in Update