This pr do two things:
1. Infer the column name if the column is expression in `select into outfile`. The rule for column name generation can be refered in pr: #24990
2. fix bug that it will core dump if the `_schema` fails to build in the open phase in vorc_transformer.cpp
TODO:
1. Support infer the column name if the column is expression in `select into outfile` in new optimizer(Nereids).