Fixes: U4-7553 Importing Document Type doesn't respect property sort order

Handling sortOrder property in both import/export.

(cherry picked from commit 378479b4c1)

# Conflicts:
#	src/Umbraco.Core/Services/PackagingService.cs

src/Umbraco.Core/Services/EntityXmlSerializer.cs

@@ -379,6 +379,7 @@ namespace Umbraco.Core.Services
                                                    new XElement("Type", propertyType.PropertyEditorAlias),
                                                    new XElement("Definition", definition.Key),
                                                    new XElement("Tab", propertyGroup == null ? "" : propertyGroup.Name),
+                                                   new XElement("SortOrder", propertyType.SortOrder),
                                                    new XElement("Mandatory", propertyType.Mandatory.ToString()),
                                                    new XElement("Validation", propertyType.ValidationRegExp),
                                                    new XElement("Description", new XCData(propertyType.Description)));

src/Umbraco.Core/Services/PackagingService.cs

@@ -658,6 +658,7 @@ namespace Umbraco.Core.Services
                                            Description = property.Element("Description").Value,
                                            Mandatory = property.Element("Mandatory").Value.ToLowerInvariant().Equals("true"),
                                            ValidationRegExp = property.Element("Validation").Value,
+                                           SortOrder = property.Element("SortOrder").Value
                                        };
 
                 var tab = property.Element("Tab").Value;