Allow index_create to suppress index_build progress reporting

Allow index_create to suppress index_build progress reporting

A future REPACK patch wants a way to suppress index_build doing its
progress reports when building an index, because that would interfere
with repack's own reporting; so add an INDEX_CREATE_SUPPRESS_PROGRESS
bit that enables this.

Furthermore, change the index_create_copy() API so that it takes flag
bits for index_create() and passes them unchanged.  This gives its
callers more direct control, which eases the interface -- now its
callers can pass the INDEX_CREATE_SUPPRESS_PROGRESS bit directly.  We
use it for the current caller in REINDEX CONCURRENTLY, since it's also
not interested in progress reporting, since it doesn't want
index_build() to be called at all in the first place.

One thing to keep in mind, pointed out by Mihail, is that we're not
suppressing the index-AM-specific progress report updates which happen
during ambuild().  At present this is not a problem, because the values
updated by those don't overlap with those used by commands other than
CREATE INDEX; but maybe in the future we'll want the ability to suppress
them also.  (Alternatively we might want to display how each
index-build-subcommand progresses during REPACK and others.)

Author: Antonin Houska <ah@cybertec.at>
Author: Álvaro Herrera <alvherre@kurilemu.de>
Reviewed-by: Mihail Nikalayeu <mihailnikalayeu@gmail.com>
Discussion: https://postgr.es/m/102906.1773668762@localhost