pgsql: Doc: clarify n_distinct_inherited setting

Doc: clarify n_distinct_inherited setting

There was some confusion around how to adjust the n_distinct estimates
for partitioned tables. Here we try and clarify that
n_distinct_inherited needs to be adjusted rather than n_distinct.

Also fix some slightly misleading text which was talking about table
size rather than table rows, fix a grammatical error, and adjust some
text which indicated that ANALYZE was performing calculations based on
the n_distinct settings. Really it's the query planner that does this
and ANALYZE only stores the overridden n_distinct estimate value in
pg_statistic.

Author: David Rowley <dgrowleyml(at)gmail(dot)com>
Reviewed-by: David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Backpatch-through: 13
Discussion: https://postgr.es/m/CAApHDvrL7a-ZytM1SP8Uk9nEw9bR2CPzVb+uP+bcNj=_q-ZmVw@mail.gmail.com

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/0a47f054ef8d5b9f2d9702ba1a5587777953fc7c

Modified Files
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doc/src/sgml/ref/alter_table.sgml | 34 ++++++++++++++++------------------
1 file changed, 16 insertions(+), 18 deletions(-)