Support safe navigation operator in spel operators/functions

[sebakerckhof]

Is your feature request related to a problem? Please describe.
I would like to use the safe navigation operator in combination with spel operators and functions like: .contains(), .toLowerCase(), .endsWith() etc, so I can apply them safely to variables that might be null.

Describe the solution you'd like
Maybe we could maybe have something similar to fieldSeperator?

Describe alternatives you've considered
I've tried overwriting the spelOp in the operators like: ${0}.endsWith(${1}) -> ${0}?.endsWith(${1}), this throws errors when importing. I think the ? is reserved for another use in the parsing.

Currently I'm just running regexes on import/export to transform everything from and to the safe navigation operator, but that's obviously not such a neat solution.