[NUCRDBMS-811] Fix enum constraint values when using getValue extension
[NUCRDBMS-809] Contrib for getValue, but extended to be not just for
simple Enum fields
Merge commit 'f951ecaebcf0baf172e5fe57bb362572fb8fd738' into CITC

Conflicts:
	src/main/java/org/datanucleus/store/rdbms/mapping/java/EnumMapping.java
	src/main/java/org/datanucleus/store/rdbms/sql/expression/EnumLiteral.java