Reflect included columns as dialect_options

Reflect included columns as dialect_options

Fixed reflection of covering indexes to report ``include_columns`` as part
of the ``dialect_options`` entry in the reflected index dictionary, thereby
enabling round trips from reflection->create to be complete. Included
columns continue to also be present under the ``include_columns`` key for
backwards compatibility.

Fixes: #7382
Change-Id: I4f16b65caed3a36d405481690a3a92432b5efd62