FunctionName description for DefaultFunctionFactory are empty

The DefaultFunctionFactory advertises the Functions that can be found using Factory SPI on the classpath). Currently this class produces a bare bones description for FunctionName; where the arguments are described as "arg1","arg1","arg2",...

This improvement represents adding the FunctionName information to the implementations so that DefaultFunctionFactory can have a better description.

Using:

• XXXFunction.NAME - as a static final constant (as per the implementation convention for Functions)
• FunctionExpression.getFunctionName() - allowing access to the above

There is a separate proposal up; for adding a Function.getFunctionName() method; this does not impact on the grunt work covered by this improvement. It would only make accessing this grunt work easier for the casual user.