REPO-5549 Fix: Local transformer names must exist and be unique docli… (#264)

* REPO-5549 Fix: Local transformer names must exist and be unique doclib Read from ... when overriding a Local transform.

* Problem was that there were two conflicting pieces of code in play in the LocalTransformRegistry.register method. One that checked for duplicate T-Engine names and the other that allowed transforms to be overridden if they had the same name.
* The code checking for duplicate names needed an extra clause to only look at T-Engines (they have a T-Engine url associated with them).
* The code that overrode transforms then worked, but still had issues as the supported source to target mimetypes, priorities and max sizes were not cleared.
* It turned out to be simpler to split the original LocalTransformRegistry.register method into two. Extracting a new method into CombinedConfig.removeOverriddenOrInvalidTransformers that discarded invalid or overridden config before the list of supported source to target mimetypes was created rather than try to fix them up later. This is why there appear to be quite a few changes.
* More extensive unit tests were also added.

data-model/src/main/java/org/alfresco/util/ConfigScheduler.java

@@ -2,7 +2,7 @@
  * #%L
  * Alfresco Repository
  * %%
- * Copyright (C) 2005 - 2020 Alfresco Software Limited
+ * Copyright (C) 2005 - 2021 Alfresco Software Limited
  * %%
  * This file is part of the Alfresco software.
  * If the software was purchased under a paid Alfresco license, the terms of
@@ -57,7 +57,10 @@ public abstract class ConfigScheduler<Data>
     public static class ConfigSchedulerJob implements Job
     {
         @Override
-        public void execute(JobExecutionContext context) throws JobExecutionException
+        // Synchronized has little effect in normal operation, but on laptops that are suspended, there can be a number
+        // of Threads calling execute concurrently without it, resulting in errors in the log. Theoretically possible in
+        // production but not very likely.
+        public synchronized void execute(JobExecutionContext context) throws JobExecutionException
         {
             JobDataMap dataMap = context.getJobDetail().getJobDataMap();
             ConfigScheduler configScheduler = (ConfigScheduler)dataMap.get(CONFIG_SCHEDULER);