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/coreplugin/vcsmanager.cpp

@@ -544,7 +544,7 @@ void CorePlugin::testVcsManager()
 
     // From VCSes:
     int expectedCount = 0;
-    for (const QString &result : qAsConst(results)) {
+    for (const QString &result : std::as_const(results)) {
         // qDebug() << "Expecting:" << result;
 
         const QStringList split = result.split(QLatin1Char(':'));