improve DEBUG1 logging of parallel workers for CREATE INDEX?

While reviewing patch [1], I realized that the DEBUG1 message
for CREATE INDEX could do better in providing information
about parallel workers launched. Currently, the message just
shows how many workers are planned, but a user may want
to ensure that they have the appropriate number of workers
launched as well when they enable DEBUG1 logging.

Therefore, I want to suggest that instead of:

postgres=# CREATE INDEX tbl_c1 ON tbl(c1);
DEBUG: building index "tbl_c1" on table "tbl" with request for 2
parallel workers
DEBUG: index "tbl_c1" can safely use deduplication
CREATE INDEX

to enhance the message to:

postgres=# create index tbl_c1 on tbl(c1);
DEBUG: building index "tbl_c1" on table "tbl"
DEBUG: launched 0 parallel vacuum workers for index vacuuming (planned: 2)
DEBUG: index "tbl_c1" can safely use deduplication
CREATE INDEX
postgres=#

I prepared a simple patch, attached, for this. The log message matches
the format
used in VACUUM VERBOSE ( for consistency sake ).

Also, I think the documentation in [2] should be updated to mention that DEBUG1
can be used to view parallel worker usage for the build, but I have
not included it in
the patch yet.

Any thoughts?

[1] https://www.postgresql.org/message-id/CAA5RZ0tS%3DFmgku9%3DqCp-U4EBC-dqVtj%2Bv_EGrKV_NA%3DTHnUDsQ%40mail.gmail.com

[2] https://www.postgresql.org/docs/current/sql-createindex.html

Regards,

Sami Imseih
Amazon Web Services (AWS)