`columns_for_distinct` might need some adjustments

[joaquinco]

I'm facing some issues when this method is called (OracleEnhancedAdapter#columns_for_distinct(columns, orders)) with Rails 8.0.4.

In particual the two issues I see are:

1. Since Rails 7.1 added support for composite primary keys the first attribute is (can be) a list of columns which is interpolated as is into the SQL query resulting in invalid syntax
2. It's not stripping out "NULLS FIRST" or "NULLS LAST" from the order by clauses, also resulting in invalid syntax

I think the first issue can be solved by joinin columns by a comma and the latter by copying postgres' solution.

I can create a PR later when I have time.

[akostadinov]

Is this issue fixed by #2480 ?

[joaquinco]

@akostadinov the first issue is solved there

[akostadinov]

It would help if you write a test case using the issue template. Or maybe a PR :) I have no idea how to reproduce this. I'm not a maintainer, just helping keep the project alive as there doesn't seem to be wide interest lately.