Support localized infinity and NaN representations

The CLDR provides localized versions (alongside those for decimal and grouping separators, %, +, − and the delimiter for the exponential part of a mantissa-exponent number format) of infinity and NaN.
In en.xml, the infinity is the ∞ symbol; en_US_POSIX.xml over-rides that as INF.
We could use these data from CLDR to provide locale-appropriate representations of non-finite values in QLocale, while retaining the C locale's "inf" and "nan" in QString and QByteArray.