pgsql: Add pg_column_toast_chunk_id().

Add pg_column_toast_chunk_id().

This function returns the chunk_id of an on-disk TOASTed value.  If
the value is un-TOASTed or not on-disk, it returns NULL.  This is
useful for identifying which values are actually TOASTed and for
investigating "unexpected chunk number" errors.

Bumps catversion.

Author: Yugo Nagata
Reviewed-by: Jian He
Discussion: https://postgr.es/m/20230329105507.d764497456eeac1ca491b5bd%40sraoss.co.jp

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d1162cfda885c5a8cb9cebfc8eed9f1d76855e83

Modified Files
--------------
doc/src/sgml/func.sgml                       | 17 ++++++++++++
src/backend/utils/adt/varlena.c              | 41 ++++++++++++++++++++++++++++
src/include/catalog/catversion.h             |  2 +-
src/include/catalog/pg_proc.dat              |  3 ++
src/test/regress/expected/misc_functions.out | 16 +++++++++++
src/test/regress/sql/misc_functions.sql      | 12 ++++++++
6 files changed, 90 insertions(+), 1 deletion(-)