Transfer statistics during pg_upgrade.

Transfer statistics during pg_upgrade.

Add support to pg_dump for dumping stats, and use that during
pg_upgrade so that statistics are transferred during upgrade. In most
cases this removes the need for a costly re-analyze after upgrade.

Some statistics are not transferred, such as extended statistics or
statistics with a custom stakind.

Now pg_dump accepts the options --schema-only, --no-schema,
--data-only, --no-data, --statistics-only, and --no-statistics; which
allow all combinations of schema, data, and/or stats. The options are
named this way to preserve compatibility with the previous
--schema-only and --data-only options.

Statistics are in SECTION_DATA, unless the object itself is in
SECTION_POST_DATA.

The stats are represented as calls to pg_restore_relation_stats() and
pg_restore_attribute_stats().

Author: Corey Huinker, Jeff Davis
Reviewed-by: Jian He
Discussion: https://postgr.es/m/CADkLM=fzX7QX6r78fShWDjNN3Vcr4PVAnvXxQ4DiGy6V=0bCUA@mail.gmail.com
Discussion: https://postgr.es/m/CADkLM%3DcB0rF3p_FuWRTMSV0983ihTRpsH%2BOCpNyiqE7Wk0vUWA%40mail.gmail.com