Full pattern matching support

[eregon]

Pattern Matching is currently partially implemented in TruffleRuby.
Specifically, array pattern matching is implemented but hash pattern matching not yet.
Currently array pattern matching is enabled by passing the --pattern-matching flag, to avoid exposing only a subset of it and ease detection of "is pattern matching supported?".

We'll implement full pattern matching support (without any flag) after #3117 is done.

[eregon]

This will be fixed for 24.0.