Add Original property in IProperty.

Author: H1Gdev

src/ExCSS/StyleProperties/IProperty.cs

@@ -4,6 +4,7 @@ public interface IProperty : IStylesheetNode
     {
         string Name { get; }
         string Value { get; }
+        string Original { get; }
         bool IsImportant { get; }
     }
 }

src/ExCSS/StyleProperties/Property.cs

@@ -31,6 +31,8 @@ internal bool TrySetValue(TokenValue newTokenValue)
 
         public string Value => DeclaredValue != null ? DeclaredValue.CssText : Keywords.Initial;
 
+        public string Original => DeclaredValue != null ? DeclaredValue.Original.Text : Keywords.Initial;
+
         public bool IsInherited => (_flags & PropertyFlags.Inherited) == PropertyFlags.Inherited && IsInitial ||
                                    DeclaredValue != null && DeclaredValue.CssText.Is(Keywords.Inherit);