REINDEX not updating partition progress

Hi,

While working on CIC for partitioned tables [1], I noticed that REINDEX
for partitioned tables is not tracking keeping progress of partitioned
tables, so I'm creating a separate thread for this fix as suggested.

The way REINDEX for partitioned tables works now ReindexMultipleInternal
treats every partition as an independent table without keeping track of
partition_done/total counts, because this is just generic code for
processing multiple tables. The patch addresses that by passing down the
knowledge a flag to distinguish partitions from independent tables
in ReindexMultipleInternal and its callees. I also noticed that the
partitioned CREATE INDEX progress tracking could also benefit from
progress_index_partition_done function that zeroizes params in addition
to incrementing the counter, so I applied it there as well.

[1]
https://www.postgresql.org/message-id/55cfae76-2ffa-43ed-a7e7-901bffbebee4%40gmail.com