consider the window function:
```sql
substr(
ref_1.cp_type,
sum(CASE WHEN ref_1.cp_type = 0 THEN 3 ELSE 2 END) OVER (),
1)
```
Before the pr, only "CASE WHEN ref_1.cp_type = 0 THEN 3 ELSE 2 END" is pushed down.
But both "ref_1.cp_type" and "CASE WHEN ref_1.cp_type = 0 THEN 3 ELSE 2 END"
should be pushed down.
This pr fix it
we should not plan any Filter or Project above CteAnchor, because there are project or filter under anchor sometimes.
and the whole plan can not translate to a valid plan for BE.
1. remove unnecessary project node above scan node.
2. fix in subquery may be recognized as scalar subquery bug
3. fix some Quantile related functions' return type bug
