Fixes #2489. New ScrollSlider and ScrollBar - Any View can have scrollbars easily

[tig]

This is based on @BDisp's awesome work in #3498 and #3798. Supplants #3811.

Fixes

• Fixes Create new ScrollBar based on a new Scroll and remove ScrollBarView/ScrollView #2489
• Fixes HexView - Upgrade to use Content Area for scrolling #3825

Proposed Changes/Todos

• Port @BDisp's work to Fixes #3761, #2886, #3780, #3485, #3622, #3413, #2995 - Draw and Layout performance/correctness #3798.
• Polish ScrollSlider
• Update Scroll to have ContentPosition and SliderPosition ++
• Update ScrollBar to be based on Scroll and just useButton
• Update unit tests
• Rebuild CharMap to use the new Scrollbar and demonstrate: Content area with headers, full keyboard integration, scrolling with > 1 increments (horizontal - 3 columns per).
• Update Scroll and ScrollBar scenarios
• Fix AllViewsTester so it can test scrollbars
• Update Scrolling Scearnio
• Update ContentScrolling scenario
• Update View.ScrollBar.cs to be cleaner
• Remove ScrollView and ScrollBarView
• Remove REPONDER!!!!
• Fix scenarios that used to use ScrollView
• Update HexView to use

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]

This is ready for review!

Please read ./docfx/docs/scrolling.md first.

Reviewing the diff for HexView.cs and HexEditor.cs will really illustrate the new API and how much simpler things are now.

[tig]

Thanks for reviewing @BDisp.

Any quesitons?