Add domain check and update registration type extensions

This completes the command extensions for the regType 0.2 extension.
Up next will be the response extensions.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=123322887

javatests/google/registry/flows/domain/DomainCheckFlowTest.java

@@ -408,4 +408,14 @@ public class DomainCheckFlowTest
     setEppInput("domain_check_fee_invalid_command.xml");
     runFlow();
   }
+
+  @Test
+  public void testSuccess_regTypeExtensionValidates() throws Exception {
+    setEppInput("domain_check_regtype.xml");
+    persistActiveDomain("example1.tld");
+    doCheckTest(
+        create(false, "example1.tld", "In use"),
+        create(true, "example2.tld", null),
+        create(true, "example3.tld", null));
+  }
 }