Add Upgrade handler to upgrade from 7.2 to 7.3

Author: alex-kulakov

Orm/Xtensive.Orm.Tests/Upgrade/LegacyUpgrade/GeneratorUpgrade/Model.cs

@@ -13,6 +13,11 @@
 
 namespace Xtensive.Orm.Tests.Upgrade.LegacyUpgrade.GeneratorUpgrade
 {
+  public class CustomUpgrdeHandler: UpgradeHandler
+  {
+    public override bool CanUpgradeFrom(string oldVersion) => true;
+  }
+
   namespace ReferenceModel.Part1
   {
     [HierarchyRoot]

Orm/Xtensive.Orm.Tests/Upgrade/LegacyUpgrade/GeneratorUpgrade/SimpleSchemaTest.cs

@@ -433,13 +433,15 @@ protected virtual void InitializeGenerators(DomainConfiguration configuration, l
 
     private void CreateDb(bool defaultGeneratorSettings, bool lessGenerators = false, long seedIncrease = 0, long cacheSizeIncrease = 0)
     {
-      var config = BuildDomainConfiguration();
-      var driver = TestSqlDriver.Create(config.ConnectionInfo);
+      var config = BuildDomainConfiguration().Clone();
+      config.Types.Register(typeof(CustomUpgrdeHandler));
 
       // clean db - deletes all the tables except for metadata tables
       // tables from previous tests are unpredictable and this is reliable thought expensive way of cleaning :-)
       using (var domain = Domain.Build(config)) { }
 
+      var driver = TestSqlDriver.Create(config.ConnectionInfo);
+
       //complete removal
       using (var connection = driver.CreateConnection()) {
         connection.Open();