Reduce usage of QStringRef::toString() in texttomodelmerger.cpp.

Change-Id: I2c42e714d916696cfa1e16575665ee48a42dccac
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>
Reduce usage of QStringRef::toString() in debuggertooltipmanager.cpp.

Change-Id: I5236df01aec5a5a173ea81d50330f0255603acad
Reviewed-by: hjk <hjk121@nokiamail.com>