Fix build and tests.

- _appendXf as single expression and fix require order for bulid
- foldl uses _xwrap for use with functions
- _dispatchable accepts function for use in _groupBy
- _isIterable uses _symIterator
- Fix filter/map to use _dispatchable appropriately
- Curry _xany, _xfilter, _xmap for use with _dispatchable
- Fix idx lint warning in _arrayReduce
- Remove no longer supported transformer dispatch test