AnnotationModel.cleanup() uses inefficient iteration over map, take 2

AnnotationModel.cleanup() will lock on the map while iterating over map
and iterate via forEach() instead to iterate over keys if possible.

This halves iteration time spent in cleanup() on huge annotation models.

Fixes #892

bundles/org.eclipse.text/src/org/eclipse/jface/text/source/AnnotationModel.java

@@ -640,13 +640,25 @@ private void cleanup(boolean fireModelChanged, boolean forkNotification) {
 			fDocumentChanged= false;
 
 			ArrayList<Annotation> deleted= new ArrayList<>();
-			Iterator<Annotation> e= getAnnotationMap().keySetIterator();
 			IAnnotationMap annotations= getAnnotationMap();
-			while (e.hasNext()) {
-				Annotation a= e.next();
-				Position p= annotations.get(a);
-				if (p == null || p.isDeleted())
-					deleted.add(a);
+			Object mapLock = annotations.getLockObject();
+
+			if (mapLock == null) {
+				Iterator<Annotation> e= annotations.keySetIterator();
+				while (e.hasNext()) {
+					Annotation a= e.next();
+					Position p= annotations.get(a);
+					if (p == null || p.isDeleted())
+						deleted.add(a);
+				}
+			} else {
+				synchronized (mapLock) {
+					annotations.forEach((a, p) -> {
+						if (p == null || p.isDeleted()) {
+							deleted.add(a);
+						}
+					});
+				}
 			}
 
 			if (fireModelChanged && forkNotification) {