[JAVA][FR]Support pattern matching in generated Parser code

[pheonixblade9]

In generated Parser code, explicit casts are used, when pattern matching has been available since JDK16: https://openjdk.org/jeps/394

For example:

    @Override
    public void enterRule(ParseTreeListener listener) {
      if (listener instanceof MyListener) ((MyListener) listener).enterSomeRule(this);
    }

could be changed to

    @Override
    public void enterRule(ParseTreeListener listener) {
      if (listener instanceof MyListener listener1) listener.enterSomeRule(this);
    }

to avoid the extra downcast.

This would definitely require testing to determine if this is actually a performance benefit, but if it's a wash, it seems reasonable to avoid extra casting when you are already checking the type via instanceof.

If nothing else, it simplifies the generated code slightly!