Port from qAsConst() to std::as_const()

We've been requiring C++17 since Qt 6.0, and our qAsConst use finally
starts to bother us (QTBUG-99313), so time to port away from it
now.

Since qAsConst has exactly the same semantics as std::as_const (down
to rvalue treatment, constexpr'ness and noexcept'ness), there's really
nothing more to it than a global search-and-replace.

Task-number: QTBUG-99313
Change-Id: I88edd91395849574436299b8badda21bb93bea39
Reviewed-by: hjk <hjk@qt.io>

src/plugins/valgrind/callgrindvisualisation.cpp

@@ -383,7 +383,7 @@ void Visualization::populateScene()
 
     // add the canvas elements to the scene
     qreal used = sceneHeight * 0.1;
-    for (const Pair &cost : qAsConst(costs)) {
+    for (const Pair &cost : std::as_const(costs)) {
         const QModelIndex &index = cost.first;
         const QString text = index.data().toString();