Put multiple QML profiling messages into one object where possible

As most of the QML profiling messages only use a small subset of the
available fields in QQmlProfilerData we can
a, reduce the size of QQmlProfilerData by using unions
b, put multiple messages into one object where their data doesn't
   overlap
Furthermore we can add another field for saving QUrl members in
QQmlProfilerData so that we can combine more different messages
and don't have to convert from QUrl to QString while profiling. This
should reduce the impact of the profiling code on the performance
of the application being profiled.

Task-number: QTBUG-35315
Change-Id: Iecd61e90cc8490d2efbbb381391d98dfee61d3cd
Reviewed-by: Michael Brasser <michael.brasser@live.com>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>