Fixes #2493. Move all layout code out of View (and Toplevel) into a layout helper class

[tig]

Fixes #2493 - Move all layout code out of View (and Toplevel) into a layout helper class
Fixes # - Renames Mdi to Overlapped; reorganzies Overlapped related code in prep for #2502
Fixes a ton of API Docs.
Renames unclear APIs.

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

[BDisp]

@tig thanks for awesome work.

[tig]

@tig thanks for awesome work.

Hopefully this all helps us more easily maintain all this code!

You ok with the Mdi -> Overlapped rename?

[BDisp]

Hopefully this all helps us more easily maintain all this code!

For sure it will be.

You ok with the Mdi -> Overlapped rename?

It's fine to me.