Also make InnoDB thinks that /*/ only starts a comment. (Bug #53644).

struct trx_struct: Add mysql_query_len.

ha_innodb.cc: Use trx_query_string() instead of trx_query() and
initialize trx->mysql_query_len.

INNOBASE_COPY_STMT(thd, trx): New macro, to initialize
trx->mysql_query_str and trx->mysql_query_len.

dict_strip_comments(): Add and observe the parameter sql_length. Treat
/*/ as the start of a comment.

dict_create_foreign_constraints(), row_table_add_foreign_constraints():
Add the parameter sql_length.