regr_count should return an int

[Michael-J-Ward]

Describe the bug

regr_count currently returns a Float64.

To Reproduce

DataFusion CLI v40.0.0
> select regr_count(1, 1);
+-------------------------------+
| regr_count(Int64(1),Int64(1)) |
+-------------------------------+
| 1.0                           |
+-------------------------------+
1 row(s) fetched. 
Elapsed 0.011 seconds.

> select arrow_typeof(regr_count(1, 1));
+---------------------------------------------+
| arrow_typeof(regr_count(Int64(1),Int64(1))) |
+---------------------------------------------+
| Float64                                     |
+---------------------------------------------+
1 row(s) fetched. 
Elapsed 0.001 seconds.

Expected behavior

Consistent with postgres, it should return Int64 or Uint64

https://www.postgresql.org/docs/9.4/functions-aggregate.html

Additional context

No response