Add a FEEL REPL to KIE Sandbox

[tiagobento]

Originally reported by @porcelli

As a user I want to a simple user interface to test/interact with FEEL expressions in a REPL format.

[tiagobento]

@porcelli That's indeed a nice feature... we can add a new Tab do the DMN Editor where users can "play" with FEEL, without changing the DMN model itself, but having access to what the open DMN model has available, like BKMs and Decision Services, for example. WDYT?

[porcelli]

liked the idea; leverage the context of the current state of the editor to provide more to the user;

however I still would like to see a plain REPL that user can just play integrated into this