pgsql: doc: PG 16 relnotes, misc updates

doc: PG 16 relnotes, misc updates

* document to_reg* accepting OIDs
* document pg_log_standby_snapshot()
* document pg_input_is_valid() and pg_input_error_info()
* handle rename of function to pg_split_walfile_name()
* fix character encoding problem for Przemyslaw Sztoch
* remove partition section

Reported-by: jian he, Tom Lane, Bertrand Drouvot

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/cf109ffc205063f82258e0643588491a153c3a45

Modified Files
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doc/src/sgml/release-16.sgml | 102 +++++++++++++++++++++++++++----------------
1 file changed, 64 insertions(+), 38 deletions(-)