Reverse order of values when upserting

I contributed two tests to Rails because I was not sure how `insert_all` and `upsert_all` should behave with duplicate identifiers.

For `insert_all`, all DBMS only insert the first value. For `upsert_all`, PostgreSQL throws an error in this scenario, but with sqlite and MySQL, the last entry ends up in the database.

For now, I do not have a smarter idea than reversing the `inserts`, which ultimately provide the `values_list`. Adding `MAX` would be another, but I fear the SQL query would get much more complicated.

Author: andyundso

Diff for: lib/active_record/connection_adapters/sqlserver/database_statements.rb

@@ -169,6 +169,8 @@ def build_insert_sql(insert) # :nodoc:
         end
 
         def build_sql_for_merge_insert(insert:, insert_all:, columns_with_uniqueness_constraints:) # :nodoc:
+          insert_all.inserts.reverse! if insert.update_duplicates?
+
           sql = <<~SQL
             MERGE INTO #{insert.model.quoted_table_name} WITH (UPDLOCK, HOLDLOCK) AS target
             USING (