(split) Add readString and writeString methods to QDataStream and fix FrideMagnets to use the new API.
(split) Add readString and writeString methods to QDataStream and fix FrideMagnets to use the new API.

[git-p4: depot-paths = "//depot/qtjambi/main/": change = 261155]

qt-generator/qt-generator,qt-generator/qt-generator,qt-generator/qt-generator