Support str_to_date function push down

Need to take care of the performance issue. Related optimization PR for date_format(https://github.com/pingcap/tics/pull/1337) (inverse function for str_to_date).

PR to master (and 5.1.0)
tiflash: https://github.com/pingcap/tics/pull/1961
tidb: https://github.com/pingcap/tidb/pull/25095