psql: Fix name quoting on extended statistics

psql: Fix name quoting on extended statistics

Per our message style guidelines, for human consumption we quote
qualified names as a whole rather than each part separately; but commits
bc085205c8a4 introduced a deviation for extended statistics and
a4d75c86bf15 copied it.  I don't agree with this policy applying to
names shown by psql, but that's a poor reason to deviate from the
practice only in two obscure corners, so make said corners use the same
style as everywhere else.

Backpatch to 14.  The first of these is older, but I'm not sure we want
to destabilize the psql output in the older branches for such a small
thing.

Discussion: https://postgr.es/m/20210828181618.GS26465@telsasoft.com