Standardize on all the char* arguments of qtestlib being UTF-8

It happened ( QTBUG-80527 ) that unicode characters (the degree symbol of QCoordinate) were being passed through .toLatin1() causing corrupt data, before being passed as const char * to the description argument of QTestResult::verify().

To avoid these corruptions, we should say that all const char * arguments of qtestlib accept only UTF-8 encoded strings, and change all conversions to use .toUtf8().

Another thing we could do is add QString overloads to verify(), see QTBUG-81473.

Edward Welbourne Tor Arne Vestbø as we discussed.