EUC_CN, EUC_JP, EUC_KR, EUC_TW: Skip U+00A0 tests instead of failing.

EUC_CN, EUC_JP, EUC_KR, EUC_TW: Skip U+00A0 tests instead of failing.

Settings that ran the new test euc_kr.sql to completion would fail these
older src/pl tests.  Use alternative expected outputs, for which psql
\gset and \if have reduced the maintenance burden.  This fixes
"LANG=ko_KR.euckr LC_MESSAGES=C make check-world".  (LC_MESSAGES=C fixes
IO::Pty usage in tests 010_tab_completion and 001_password.)  That file
is new in commit c67bef3f3252a3a38bf347f9f119944176a796ce.  Back-patch
to v14, like that commit.

Discussion: https://postgr.es/m/20260217184758.da.noahmisch@microsoft.com
Backpatch-through: 14