Fix for multi-threading issues in AnnotationMap

- added synchronize block to methods in AnnotationModel, wherever reads
/ writes could happen in multiple threads.
- changed execution order, to be able to synchronize only necessary code
blocks.

Co-authored-by: Andrey Loskutov <loskutov@gmx.de>

Author: mehmet-karaman

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

@@ -679,7 +679,7 @@ private void cleanup(boolean fireModelChanged, boolean forkNotification) {
 			ArrayList<Annotation> deleted= new ArrayList<>();
 			IAnnotationMap annotations= getAnnotationMap();
 			Object mapLock = annotations.getLockObject();
-			Assert.isNotNull(mapLock);
+
 			synchronized (mapLock) {
 				annotations.forEach((a, p) -> {
 					if (p == null || p.isDeleted()) {
@@ -690,7 +690,7 @@ private void cleanup(boolean fireModelChanged, boolean forkNotification) {
 
 			if (fireModelChanged && forkNotification) {
 				removeAnnotations(deleted, false, false);
-				synchronized (getLockObject()) {
+				synchronized (mapLock) {
 					if (fModelEvent != null) {
 						final AnnotationModelEvent event = fModelEvent;
 						fModelEvent = null;