In `main`, `LegacyPluginTest` fails (after bumping `log4j2-logstash-layout.version` to `1.0.5` <https://github.com/apache/logging-log4j2/pull/1586>) due to missing `ENABLE_THREADLOCALS` static field in `org.apache.logging.log4j.core.util.Constants`. 287ee839 is responsible for this change and there are more constants removed. Given this breaks backward compatibility, what shall we do?
Note that my question is not merely limited to the `Constants` class. Otherwise I would have simply introduced those fields back. I bet I can find dozens of such breaking changes if I search long enough.
