Support non-FEEL function kind according to the spec

[barmac]

Is your feature request related to a problem? Please describe.

In the case of non-FEEL languages, one has to use a context with strictly specified keys as described at https://www.omg.org/spec/DMN/1.3/PDF#page=132

In the WIP implementation of the boxed expression, we allow any expression inside of such function.

Describe the solution you'd like

Enforce context with well-defined keys for non-FEEL languages.

Describe alternatives you've considered

Leave it as is.

Additional context

#852 (comment)