Fixes U4-1480 ContentBase.SetPropertyValue has no override for long datatype

src/Umbraco.Core/Models/ContentBase.cs

@@ -309,6 +309,17 @@ namespace Umbraco.Core.Models
             SetValueOnProperty(propertyTypeAlias, value);
         }
 
+        /// <summary>
+        /// Sets the <see cref="System.Int64"/> value of a Property
+        /// </summary>
+        /// <param name="propertyTypeAlias">Alias of the PropertyType</param>
+        /// <param name="value">Value to set for the Property</param>
+        public virtual void SetPropertyValue(string propertyTypeAlias, long value)
+        {
+            string val = value.ToString();
+            SetValueOnProperty(propertyTypeAlias, val);
+        }
+
         /// <summary>
         /// Sets the <see cref="System.Boolean"/> value of a Property
         /// </summary>