MDEV 13679 Enabled sequences to be used in DEFAULT

Other changes done to get this to work:
- Added 'internal_tables' to TABLE object to list which sequence tables
  is needed to use the table.
- Mark any expression using DEFAULT() with LEX->default_used.
  This is needed when deciding if we should open internal sequence
  tables when a table is opened (we don't need to open sequence tables
  if the main table is only used with SELECT).
- Create_and_open_temporary_table() can now also open all internal
  sequence tables.
- Added option MYSQL_LOCK_USE_MALLOC to mysql_lock_tables()
  to force memory allocation to be used with malloc instead of
  memroot.
- Added flag to MYSQL_LOCK to remember if allocation was done with
  malloc or memroot (makes code simpler and safer).
- init_one_table_for_prelocking() now takes argument for what lock to
  use instead of it's a routine or something else.
- Renamed prelocking placeholders to make them more understandable as
  they are now used in more code.
- Changed test in check_lock_and_start_stmt() if found table has correct
  locks. The old test didn't work for tables that has lock
  TL_WRITE_ALLOW_WRITE, which is what sequence tables are using.
- Added VCOL_NOT_VIRTUAL option to ensure that sequence functions can't
  be used with virtual columns
- More sequence tests

sql/sql_class.h

@@ -373,8 +373,9 @@ public:
 typedef struct st_mysql_lock
 {
   TABLE **table;
-  uint table_count,lock_count;
   THR_LOCK_DATA **locks;
+  uint table_count,lock_count;
+  uint flags;
 } MYSQL_LOCK;
 
 
@@ -4406,7 +4407,8 @@ public:
                                    const char *path,
                                    const char *db,
                                    const char *table_name,
-                                   bool open_in_engine);
+                                   bool open_in_engine,
+                                   bool open_internal_tables);
 
   TABLE *find_temporary_table(const char *db, const char *table_name);
   TABLE *find_temporary_table(const TABLE_LIST *tl);