*sum: Fix locales fetching from checksum_common after installation

[RenjiSann]

Fixes the issue raised in #10142 (comment) and #10549

Basically, this change does 3 things:

• Embeds checksum_common en_US locales in uucore at build time if necessary.
• Make init_localization look for checksum_common locales.
• Install extra locales for checksum_common when running make install.

cc @oech3

[oech3]

We have sum command, but is .ends_with("sum") OK if we don't use ck-* translations?

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/shuf/shuf-reservoir (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/sort/sort-stale-thread-mem (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/basenc/bounded-memory is now passing!

[RenjiSann]

We have sum command, but is .ends_with("sum") OK if we don't use ck-* translations?

Good catch. It's not problematic: we will just include the common locales for it even though it doesn't need it.
Actually, I never looked at sum, maybe we can port it to the common implementation as well

[oech3]

Does release/debug profile specific regression test works correctly?

[RenjiSann]

Does release/debug profile specific regression test works correctly?

I'm not sure it is actually possible to test the release installation.