MDEV-22164 without validation for exchange partition/convert in

1. WITHOUT/WITH VALIDATION may be added to EXCHANGE PARTITION or CONVERT TABLE:

  alter table tp exchange partition p1 with table t with validation;
  alter table tp exchange partition p1 with table t; -- same as with validation
  alter table tp exchange partition p1 with table t without validation;

2. Optional THAN keyword for RANGE partitioning. Normally you type:

  create table tp (a int primary key) partition by range (a) (
    partition p0 values less than (100),
    partition p1 values less than maxvalue);

  Now you may type (PARTITION keyword is also optional):

  create table tp (a int primary key) partition by range (a) (
    p0 values less (100),
    p1 values less maxvalue);

sql/sql_partition.cc

@@ -4107,6 +4107,9 @@ bool verify_data_with_partition(TABLE *table, TABLE *part_table,
   DBUG_ASSERT(table && table->file && part_table && part_table->part_info &&
               part_table->file);
 
+  if (table->in_use->lex->without_validation)
+    DBUG_RETURN(false);
+
   /*
     Verify all table rows.
     First implementation uses full scan + evaluates partition functions for