Add some tests for encoding conversion in COPY TO/FROM
This adds a couple of tests to trigger encoding conversion when input
and server encodings do not match in COPY FROM/TO, or need_transcoding
set to true in the COPY state data. These tests rely on UTF8 <-> LATIN1
for the valid cases as LATIN1 accepts any bytes, and UTF8 <-> EUC_JP for
some of the invalid cases where a character cannot be understood,
causing a conversion failure.
Both ENCODING and client_encoding are covered. Test suggested by Andres
Freund.
Author: Sutou Kouhei
Discussion: https://postgr.es/m/
20240206222445.hzq22pb2nye7rm67@awork3.anarazel.de