REINDEX already does full relation rewrite, this patch adds a
possibility to specify a new tablespace where new relfilenode
will be created.

Is this fine ?  It says "cannot reindex system catalogs concurrently" (once),
and hits the pg_toast tables for information_schema.  Should it skip toast
indexes (like it said) ?  Or should it REINDEX them on the same tablespace?

template1=# REINDEX DATABASE CONCURRENTLY template1 TABLESPACE pg_default;
2020-03-09 15:33:51.792 CDT [6464] WARNING:  cannot reindex system catalogs concurrently, skipping all
WARNING:  cannot reindex system catalogs concurrently, skipping all
2020-03-09 15:33:51.794 CDT [6464] WARNING:  skipping tablespace change of "pg_toast_12558_index"
2020-03-09 15:33:51.794 CDT [6464] DETAIL:  Cannot move system relation, only REINDEX CONCURRENTLY is performed.
WARNING:  skipping tablespace change of "pg_toast_12558_index"
DETAIL:  Cannot move system relation, only REINDEX CONCURRENTLY is performed.
2020-03-09 15:33:51.924 CDT [6464] WARNING:  skipping tablespace change of "pg_toast_12543_index"
2020-03-09 15:33:51.924 CDT [6464] DETAIL:  Cannot move system relation, only REINDEX CONCURRENTLY is performed.
WARNING:  skipping tablespace change of "pg_toast_12543_index"
DETAIL:  Cannot move system relation, only REINDEX CONCURRENTLY is performed.
2020-03-09 15:33:51.982 CDT [6464] WARNING:  skipping tablespace change of "pg_toast_12548_index"
2020-03-09 15:33:51.982 CDT [6464] DETAIL:  Cannot move system relation, only REINDEX CONCURRENTLY is performed.
WARNING:  skipping tablespace change of "pg_toast_12548_index"
DETAIL:  Cannot move system relation, only REINDEX CONCURRENTLY is performed.
2020-03-09 15:33:52.048 CDT [6464] WARNING:  skipping tablespace change of "pg_toast_12553_index"
2020-03-09 15:33:52.048 CDT [6464] DETAIL:  Cannot move system relation, only REINDEX CONCURRENTLY is performed.
WARNING:  skipping tablespace change of "pg_toast_12553_index"
DETAIL:  Cannot move system relation, only REINDEX CONCURRENTLY is performed.
REINDEX