callstack: Fix source code compatibility with Java 11

Change-Id: I9420d4149c9acb0dfd29cbf7b8087e6c1b4c1186
Signed-off-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/c/tracecompass/org.eclipse.tracecompass/+/204672
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Trace Compass Bot <tracecompass-bot@eclipse.org>
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>

analysis/org.eclipse.tracecompass.analysis.callstack.core/src/org/eclipse/tracecompass/internal/analysis/callstack/core/flamegraph/FlameGraphDataProvider.java

@@ -28,6 +28,7 @@
 import java.util.function.Predicate;
 import java.util.logging.Level;
 import java.util.logging.Logger;
+import java.util.stream.Collectors;
 
 import org.apache.commons.lang3.StringUtils;
 import org.eclipse.core.runtime.IProgressMonitor;
@@ -406,7 +407,7 @@ private void recursivelyAddChildren(IWeightedTreeProvider<N, E, T> wtProvider, I
         // Add the extra sites
         List<String> extraDataSets = wtProvider.getExtraDataSets();
         for (int i = 0; i < extraDataSets.size(); i++) {
-            List<WeightedTree<@NonNull N>> extraDataTrees = callSite.getExtraDataTrees(i).stream().sorted(fCctComparator2).toList();
+            List<WeightedTree<@NonNull N>> extraDataTrees = callSite.getExtraDataTrees(i).stream().sorted(fCctComparator2).collect(Collectors.toList());
             if (extraDataTrees.isEmpty()) {
                 continue;
             }