sql: forbid diff. sorting orders in ORDER BY + LIMIT

Without multi-directional iterators (to be introduced in #3309)
ORDER BY + LIMIT with different specified ordered leads to wrong
result. So for now (till #3309 is resolved) different sort
orders are forbidden in ORDER BY + LIMIT.

Close #4038

@TarantoolBot document
Title: different sorting orders in ORDER BY are forbidden now
The error will be raised if different sorting orders are
encountered.