sort: use locale decimal separator for general numeric parse

[ChrisDryden]

The only part of the tests that was failing for sort was the locale support for decimals. I figured since all of the utilities use the same library method for getting the locale separator it would be better to update the library instead of the individual function.

Ideally we will do the exact same approach for the thousands separator too, for the other GNU locale test

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/misc/sleep. tests/misc/sleep is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/seq/seq. tests/seq/seq is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/sort/sort-stale-thread-mem. tests/sort/sort-stale-thread-mem is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/tty/tty-eof. tests/tty/tty-eof is passing on 'main'. Maybe you have to rebase?
Congrats! The gnu test tests/sort/sort-float is no longer failing!

[ChrisDryden]

Darn, looks like this causes some issues

[sylvestre]

and will need some tests too :)

[ChrisDryden]

Can you take a look at some of the non-draft ones?