Added tests for further border-image subproperties
Added tests for further border-image subproperties

AngleSharp/AngleSharp,FlorianRappl/AngleSharp,zedr0n/AngleSharp.Local,FlorianRappl/AngleSharp,Livven/AngleSharp,zedr0n/AngleSharp.Local,AngleSharp/AngleSharp,AngleSharp/AngleSharp,AngleSharp/AngleSharp,FlorianRappl/AngleSharp,Livven/AngleSharp,FlorianRappl/AngleSharp,AngleSharp/AngleSharp,zedr0n/AngleSharp.Local,Livven/AngleSharp