Fixes #3273. Updates `FindDeepestView` to support `Adornment`

[tig]

Fixes

• Fixes #3273

Proposed Changes/Todos

• [x] Modify FindDeepestView to return Margin, Padding, or Border if x/y match.
• [ ] Add MouseEvent handling code to Adornment, Margin, Border, and Padding as appropriate (e.g. Adornment.MouseClick += Parent.SetFocus()).
• [ ] Add more FindDeepestView unit tests to prove this change works.
• [ ] Add support for Adornment.SubViews

Pull Request checklist:

• [x] I've named my PR in the form of "Fixes #issue. Terse description."
• [x] 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.
• [x] My code follows the Terminal.Gui library design guidelines
• [x] I ran dotnet test before commit
• [x] I have made corresponding changes to the API documentation (using /// style comments)
• [x] My changes generate no new warnings
• [x] I have checked my code and corrected any poor grammar or misspellings
• [x] I conducted basic QA to assure all features are working