MDEV-7563 Support CHECK constraint as in (or close to) SQL Standard

MDEV-10134 Add full support for DEFAULT

- Added support for using tables with MySQL 5.7 virtual fields,
  including MySQL 5.7 syntax
- Better error messages also for old cases
- CREATE ... SELECT now also updates timestamp columns
- Blob can now have default values
- Added new system variable "check_constraint_checks", to turn of
  CHECK constraint checking if needed.
- Removed some engine independent tests in suite vcol to only test myisam
- Moved some tests from 'include' to 't'. Should some day be done for all tests.
- FRM version increased to 11 if one uses virtual fields or constraints
- Changed to use a bitmap to check if a field has got a value, instead of
  setting HAS_EXPLICIT_VALUE bit in field flags
- Expressions can now be up to 65K in total
- Ensure we are not refering to uninitialized fields when handling virtual fields or defaults
- Changed check_vcol_func_processor() to return a bitmap of used types
- Had to change some functions that calculated cached value in fix_fields to do
  this in val() or getdate() instead.
- store_now_in_TIME() now takes a THD argument
- fill_record() now updates default values
- Add a lookahead for NOT NULL, to be able to handle DEFAULT 1+1 NOT NULL
- Automatically generate a name for constraints that doesn't have a name
- Added support for ALTER TABLE DROP CONSTRAINT
- Ensure that partition functions register virtual fields used. This fixes
  some bugs when using virtual fields in a partitioning function

mysql-test/r/mysql57_virtual.result

@@ -0,0 +1,38 @@
+#
+# Test that we can use tables created in MySQL 5.7
+#
+SHOW CREATE TABLE mysql57_virtual;
+Table	Create Table
+mysql57_virtual	CREATE TABLE `mysql57_virtual` (
+  `a` int(11) DEFAULT NULL,
+  `b` int(11) AS ((`a` + 1)) VIRTUAL,
+  `c` int(11) AS ((`a` + 3)) PERSISTENT
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+insert into mysql57_virtual (a) values (1),(2);
+select * from mysql57_virtual;
+a	b	c
+1	2	4
+2	3	5
+alter online table mysql57_virtual comment "I am now a MariaDB table";
+ERROR 0A000: LOCK=NONE is not supported. Reason: COPY algorithm requires a lock. Try LOCK=SHARED.
+alter table mysql57_virtual comment "I am now a MariaDB table";
+SHOW CREATE TABLE mysql57_virtual;
+Table	Create Table
+mysql57_virtual	CREATE TABLE `mysql57_virtual` (
+  `a` int(11) DEFAULT NULL,
+  `b` int(11) AS ((`a` + 1)) VIRTUAL,
+  `c` int(11) AS ((`a` + 3)) PERSISTENT
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 COMMENT='I am now a MariaDB table'
+DROP TABLE mysql57_virtual;
+#
+# Check MySQL 5.7 syntax
+#
+create table t1 (a int, b int generated always as (a+1) STORED, c int generated always as (a+2) VIRTUAL);
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) DEFAULT NULL,
+  `b` int(11) AS (a+1) PERSISTENT,
+  `c` int(11) AS (a+2) VIRTUAL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1;