Tidy up a lot of repetitive code.
Remove unused arity parameter.
Various fixes to IR JIT bootstrap.

* Handle [] args appropriately
* Don't link Java methods directly ye
* Ensure arities match or use DynamicMethod.call
* Uniform representation of site/target arity (-1 for []).
Support [] args along indy paths.
If AttrAssign is against literal 'self', no visibility check.