QLocale::formattedDataSize() is implemented wrongly

The implementation currently glues a unit after a formatted number, with a space between them.
That's fine for English, and probably quite a lot of other locales, but CLDR actually provides proper formatting information, not just the name of the unit, so we should use that information, thereby combining the fragments in a locale-appropriate way, rather than combining locale-appropriate fragments in an anglophone way.