Change array_agg to return null on no input rather than empty list

[jayzhan211]

Which issue does this PR close?

As @findepi pointed out in #11274 (comment) that most of the aggregate function does not return non-null result if no row qualified. I double check the result in Postgres and Duckdb and find out they does not return empty list for array_agg. I think we can follow the behaviour as they did.

I also hope this can make dealing with nullability simpler

1. Check the nullability of each (aggregate) function
2. Make sure nullable is helpful for logical optimizer.

Closes #.

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

The result of array agg is changed

[findepi]

why removed?

[jayzhan211]

I rewrite it to the simpler one!

[findepi]

add array_agg(distinct case on empty table

[alamb]

Looks good to me @jayzhan211 . Thank you for this PR

Also, thank you @findepi for the reviews 🙏

I double checked the answers in postgres and I believe after this PR DataFusion has consistent behavior

postgres=# create table t(a int, b float, c bigint);
ERROR:  relation "t" already exists
postgres=# drop table t;
DROP TABLE
postgres=# create table t(a int, b float, c bigint);
CREATE TABLE
postgres=# insert into t values (1, 1.2, 2);
INSERT 0 1
postgres=# select array_agg(a) from t where a > 2;
 array_agg
-----------

(1 row)

postgres=# select array_agg(b) from t where b > 3.1;
 array_agg
-----------

(1 row)

postgres=# select array_agg(c), count(1) from t where c > 3;
 array_agg | count
-----------+-------
           |     0
(1 row)

postgres=# select array_agg(distinct a) from t where a > 3;
 array_agg
-----------

(1 row)

[jayzhan211]

Thanks @alamb @findepi