Order by selected items when using distinct exists

[aidanharan]

Fixes the failing "FinderTest#test_exists_with_distinct_and_offset_and_select" test.

See failing test at https://travis-ci.org/rails-sqlserver/activerecord-sqlserver-adapter/jobs/655397653?utm_medium=notification&utm_source=github_status

The issue was introduced by rails/rails#36647

The issue was caused by ordering being removed for distinct exists queries. This is fine for other adapters but MSSQL requires ordering on the items in the select distinct.

The failing test produced the following invalid MSSQL SQL:

SELECT  DISTINCT [posts].[body] FROM [posts]  ORDER BY [posts].[id] ASC OFFSET @0 ROWS FETCH NEXT @1 ROWS ONLY

This PR produces:

SELECT  DISTINCT [posts].[body] FROM [posts]  ORDER BY [posts].[body] ASC OFFSET @0 ROWS FETCH NEXT @1 ROWS ONLY