oeqa/selftest/locales: Add selftest for locale generation/presence

[YOCTO #9070]

Add a new selftest to validate locale generation. This selftest builds a
complete target with GLIBC_GENERATE_LOCALES, IMAGE_LINGUAS,
ENABLE_BINARY_LOCALE_GENERATION set.

Signed-off-by: Louis Rannou <lrannou@baylibre.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>