minor doc issues.
Returns the chunk id of the TOASTed value, or NULL if the value is not TOASTed.
Should it be "chunk_id"?
you may place it after pg_create_logical_replication_slot entry to
make it look like alphabetical order.
There is no test. maybe we can add following to src/test/regress/sql/misc.sql
create table val(t text);
INSERT into val(t) SELECT string_agg(
chr((ascii('B') + round(random() * 25)) :: integer),'')
FROM generate_series(1,2500);
select pg_column_toast_chunk_id(t) is not null from val;
drop table val;