Improve menu layout for MenuBars

[tznind]

Also, I couldn't figure out how to add more top-level menu bar items so I had to do that by editing myView.Designer.cs directly.

Rename this command to make it clearer it is a top level menu that will be added

Adjust naming here, it can be confusing.

[tig]

Related:

• https://github.com/gui-cs/Terminal.Gui/issues/2975