The QLocale methods that report the fragments used in making up
numbers all return QChar. A note dating from before Qt5 times warned
that we need to change these to return QString (since we might need a
surrogate pair to represent the relevant characters). Give advance
warning in the documentation that this shall happen at Qt 6.
[ChangeLog][QtCore][QLocale] decimalPoint(), groupSeparator(),
percent(), zeroDigit(), negativeSign(), positiveSign() and
exponential() still return QChar but shall be changed to return
QString in Qt 6. Callers are encouraged to switch to QString early,
exploiting the QString(QChar) constructor.
Task-number: QTBUG-81053
Change-Id: Ia802c7665676ecf13669c6a6f173f2e70eac578e
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
f91af791cc