Simple bug in SimpleNamedResourceManager

The method getFieldValue(Object, String) needs to be altered to use
getDeclaredField because ResourceRegistration is now protected due to
https://issues.apache.org/jira/browse/UIMA-2102

https://github.com/apache/uima-uimafit/blob/trunk/uimafit-core/src/main/java/org/apache/uima/fit/util/SimpleNamedResourceManager.java#L204

User report: https://lists.apache.org/thread.html/b4f1df20acd7d13ba95a5aca6460a69ba53f0441250443bdf498770d@%3Cdev.uima.apache.org%3E

Needs to be fixed in such a way that it also still works with older UIMA core versions.