[V2] truecolor support

[GamerGirlandCo]

Fixes #48 - Add true color support

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]

Very good work, thanks. I think @tig would prefer you submit this PR based on the https://github.com/tig/Terminal.Gui/tree/v2_fixes_666_console_driver_dupes instead of the v2_develop branch, as @adstep did on the tig#15. Maybe it's a good idea you merge the @adstep's branch into your PR and adjust the better of the two PR and leverage your changes to the others drivers.
Please review the AttributeJsonConverter.cs changes because I think the new Attribute (-1) will getting invalid colors, as it need to get the pair´s foreground/background colors.

[GamerGirlandCo]

Please review the AttributeJsonConverter.cs changes because I think the new Attribute (-1) will getting invalid colors, as it need to get the pair´s foreground/background colors.

done!

[tig]

This will be merged as part of #2612