Support for auto-completion

[ftomassetti]

When using ANTLR to build editors, we find very valuable antlr4-c3, the library for autocompletion created by Mike Lischke.

Should we consider do one of these two things?

• Including such functionalities in ANTLR 5
• Ask Mike what kind of features would make easier to implement a similar library and what limitations in implementing autocompletion there are in ANTLR 4, preventing to get a more robust/well performing solution

[ericvergnaud]

I guess this is a sub-topic of LSP support, but definitely worth its own discussion