Add a new NuGet
- add a targets file to the nuget to warn if the platform packages were not installed
Update the pipeline:
- use build artifacts everywhere
- just disable tizen for Windows
* Removed v2.3.1 and renamed Flags to BufferFlags
* Updated some API and Doc
* Add Gtk3 views
* Reworked the samples logic
- handle the more varied project structure
- build the generated zip to test it
- always use the local nuget cache
* macOS is always Any CPU
* Rename SKWidget to SKDrawingArea for GTK#3
- this allows us to have a single moniker for docs
- it indicates that it is not quite the same as the widget in GTK#2
- is is more specific so we can have more GTK# controls
* merge all the views (except forms) into a single moniker so it is better for browsing in the docs portal
* SK3dView is not actually obsolete :)
* Add readmes to the samples
Matthew Leibowitz