Provide an overload for QTextStream::setEncoding() that accepts an arbitrary encoding name

Qt 6.4 enabled QStringEncoder/QStringDecoder to use all codecs provided by ICU (see https://doc.qt.io/qt-6/whatsnew64.html#qt-core-module ). However, as of Qt 6.6, QTextStream::setEncoding() only accepts the few encodings covered by QStringConverter::Encoding.

Adding a QTextStream::setEncoding(const char*) overload to match the QStringEncoder/QStringDecoder constructors will make it a more complete replacement for Qt 5's QTextStream::setCodec().

Use case

Without this overload, users porting from Qt 5 might need to significantly restructure their code. For example, instead of passing encoded data straight into QTextStream, they must manually pass it into to QStringDecoder first, and then pass the decoded string to QTextStream.