NIFI-3938: Added ScriptedLookupService, some refactor for reusable scripting classes

[mattyb149]

Moved some code common to scripted ControllerServices out into AbstractScriptedControllerService. Also the Scripting helper classes were in the processor package but are useful elsewhere, so I moved that and changed the visibility of some protected methods.

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[alopresto]

Reviewing...

[alopresto]

Built with contrib-check and all tests pass. With Matt's help, I created a schema registry with a defined schema, generated flowfiles with CSV formatted data (a hockey roster), and used SplitRecord with the CSVReader and CSVRecordSetWriter controller services to split the data into individual flowfiles, then used LookupRecord with ScriptedLookupService and wrote a custom Groovy implementation which performed position lookups. Finally, I output the enriched flowfiles to a ConvertRecord processor which wrote them out in JSON.

Looks very useful and I think this will make a lot of people's flows more powerful. Thanks Matt.

+1, merging.