Fixes #3652. Setting Menus causes unexpected Exception.

[BDisp]

Fixes

• Fixes Setting Menus causes unexpected Exception #3652, Fixes Some uses of the CheckStyle enum are buggy #3644

Proposed Changes/Todos

• Rename Shortcut to ShortcutKey and change type to Key
• Change HotKey type to Key
• Improving add and remove menu items dynamically
• Allow run an action in IsTopLevel menu bar item through HotKey

Pull Request checklist:

• I've named my PR in the form of "Fixes #issue. Terse description."
• My code follows the style guidelines of Terminal.Gui - if you use Visual Studio, hit CTRL-K-D to automatically reformat your files before committing.
• My code follows the Terminal.Gui library design guidelines
• I ran dotnet test before commit
• I have made corresponding changes to the API documentation (using /// style comments)
• My changes generate no new warnings
• I have checked my code and corrected any poor grammar or misspellings
• I conducted basic QA to assure all features are working

[tig]

Really great work!

[tig]

Some minor tweaks please.