Re-add synchronization to ExtItemDict. (MID-4799)

The Java synchronization was left out to make ExtItem conflicts more
visible and therefore resolvable during 3.9 development. Otherwise
they are masked by the synchronization and manifest themselves
only in e.g. clustered environment.

Unfortunately we had no time to fix them. So here we re-enable
Java synchronization for RExtItemDictionary methods.

repo/repo-sql-impl/src/main/java/com/evolveum/midpoint/repo/sql/data/common/dictionary/ExtItemDictionary.java

@@ -91,22 +91,22 @@ private void fetchItemsAttempt() {
         }
     }
 
-    @NotNull    // TODO synchronized (before release)
-    public RExtItem createOrFindItemDefinition(@NotNull ItemDefinition<?> definition, boolean throwExceptionAfterCreate) {
+    @NotNull
+    public synchronized RExtItem createOrFindItemDefinition(@NotNull ItemDefinition<?> definition, boolean throwExceptionAfterCreate) {
         return createOrFindItemByDefinitionInternal(definition, true, throwExceptionAfterCreate);
     }
 
-    @NotNull    // TODO synchronized (before release)
-    public RExtItem createOrFindItemDefinition(@NotNull ItemDefinition<?> definition) {
+    @NotNull
+    public synchronized RExtItem createOrFindItemDefinition(@NotNull ItemDefinition<?> definition) {
         return createOrFindItemByDefinitionInternal(definition, true, true);
     }
 
-    @Nullable   // TODO synchronized (before release)
-    public RExtItem findItemByDefinition(@NotNull ItemDefinition<?> definition) {
+    @Nullable
+    public synchronized RExtItem findItemByDefinition(@NotNull ItemDefinition<?> definition) {
         return createOrFindItemByDefinitionInternal(definition, false, true);
     }
 
-    @Contract("_, _, true -> !null")    // TODO synchronized (before release)
+    @Contract("_, _, true -> !null")
     private RExtItem createOrFindItemByDefinitionInternal(
             @NotNull ItemDefinition<?> definition, boolean create, boolean throwExceptionAfterCreate) {
 
@@ -173,8 +173,7 @@ private void executeAttempts(String operationName, String operationVerb, Runnabl
         }
     }
 
-    // TODO synchronized (before release)
-    public RExtItem getItemById(Integer extItemId) {
+    public synchronized RExtItem getItemById(Integer extItemId) {
         boolean fresh = fetchItemsIfNeeded();
         RExtItem extItem = itemsById.get(extItemId);
         if (extItem != null || fresh) {