[SP-1612] - Regression of PDI-13082 - Regression: MapReduce Input is missing Serializable Data Type (5.2 Suite)


No Unit tests since this is pure UI change - could break nothing.

@mattcasters @mattyb149 @brosander could you please review?

this is a 5.2 backport for https://github.com/pentaho/big-data-plugin/pull/273