Sort out tests in `aggregate.slt`

[Rachelint]

Is your feature request related to a problem or challenge?

I found tests in aggregate.slt a bit messy and the file is too big(6088 rows)... when I try add more tests of median for #13681

Maybe we should split and sort out such tests to make it clearer.

Describe the solution you'd like

I think #12525 is a good example.

And maybe we can do something like it. We can split the tests into multiple test files, and each file only contains testcases for a special aggregation function:

• Current

aggregate.slt

• After sorting out

aggregate
  init.slt.part
  min_max.slt
  median.slt
  ...

Describe alternatives you've considered

No response

Additional context

No response

[Omega359]

I noted this in #13470 (comment) ... I think a bunch of those test files could be refactored and reorganized.

[Rachelint]

I noted this in #13470 (comment) ... I think a bunch of those test files could be refactored and reorganized.

It may be great if can refactor other test files messy like it !

[logan-keede]

take