uucore/quoting_style: Add support for quoting/escaping empty strings

[sargas]

This PR adds the ability to determine quotations and/or escaping needed for empty strings. This can happen if an empty string is passed to printf.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/stdbuf (passes in this run but fails in the 'main' branch)

[RenjiSann]

Thanks !
Can you also add a test in test_printf.rs as well ?

[RenjiSann]

Please account for the clippy warning and merge the if case with the one above.

[sargas]

Made the clippy change, test_printf is next, but need some more time to figure out why this didn't pass the printf-quote test in CI (it passes locally).

The test failure appears to be from parts of the tests setting LC_ALL=$LOCALE_FR_UTF8 for multi-byte tests. Adding set -x to the test I can see that I don't even run those tests locally (they are skipped if test $LOCALE_FR_UTF8 is none, which seems strange because my understanding is that test is usually used for boolean return values, not its standard output).

From the output in GitHub Action logs, it looks like we have the correct behavior for LC_ALL=$LOCALE_FR_UTF8 but not LC_ALL=C, so it doesn't look like this is fixable with correctly handle locale.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/misc/tee is no longer failing!

[RenjiSann]

Our implementation does not handle locale setting at all for the moment. This will change in the future, but in the mean time, the implementation should stick to the LC_ALL=C behavior.

The GNU tests that rely on locale-setting are expected to fail until then.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)

[sargas]

Gotcha, thank you. So this test doesn't pass tests/printf/printf-quote (unless one does not have the French locale installed), but at least it fixes printf %q ''

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/misc/stdbuf (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/stdbuf (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/misc/tee is no longer failing!

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/stdbuf (passes in this run but fails in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/stdbuf (fails in this run but passes in the 'main' branch)

[sargas]

I've rebased this PR; it does fix tests/printf/printf-quote except for locale-specific logic, I wasn't intending to add more to this PR unless there's other code review comments

[RenjiSann]

LGTM