Checks NormalizePosixLocale on codesets, modifiers, the Latn and Cyrl script
modifiers (also where the name already has a script), names that are already
BCP-47, and C, POSIX and empty names, which must normalise to no locale.
Adds a host-only test, system_service_language_locale, for ParseTag: case
normalisation of the language, script and region subtags, the three-digit
region of es-419, variants and extensions that are ignored, and the inputs it
must reject (empty and oversized subtags, one-letter and long languages, the
POSIX underscore and codeset forms) without touching the output tag.
MarcZX10