Use pgstat_progress_update_multi_param() where possible

Use pgstat_progress_update_multi_param() where possible

This commit changes one code path in REINDEX INDEX and one code path
in CREATE INDEX CONCURRENTLY to report the progress of each operation
using pgstat_progress_update_multi_param() rather than
multiple calls to pgstat_progress_update_param().  This has the
advantage to make the progress report more consistent to the end-user
without impacting the amount of information provided.

Author: Bharath Rupireddy
Discussion: https://postgr.es/m/CALj2ACV5zW7GxD8D_tyO==bcj6ZktQchEKWKPBOAGKiLhAQo=w@mail.gmail.com