Support for safe navigation operator (aka Elvis operator aka ?:)

Looks like `myObject?:method()` is not yet recognized as valid syntax.
I'm not sure how much effort it would be to add this?
I see [Riverside's proparse fork](https://github.com/Riverside-Software/sonar-openedge/blob/develop/proparse/src/main/antlr4/imports/BaseTokenTypes.tokens) has support for "ELVIS" which I assume is this operator...