The new QStringEncoder and QStringDecoder classes
(with a common QStringConverter base class) are
there to replace QTextCodec in Qt 6.
It currently uses a trivial wrapper around the utf
encoding functionality.
Added some autotests, mostly copied from the text codec
tests.
Change-Id: Ib6eeee55fba918b9424be244cbda9dfd5096f7eb
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>