Fix mssql index column order

Fix mssql index column order

Fixed issue where the index reflection for SQL Server would
not correctly return the order of the column inside an index
when the order of the columns in the index did not match the
order of the columns in the table.
Pull request courtesy of Allen Chen.

Fixes: #12894
Closes: #12895
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/12895
Pull-request-sha: bd9bd43219f35a29eaeee81fedea452afc64eb5d

Change-Id: I45ed30bbd0fcfd4f67cb2b682ecb3a18029be2b7