- instantiation
- calling of methods and field access
- type conversions

* warn if the executor used for resizing is not available
* do not execute PolyglotEngine.Value#get if there is no executor

Also added a debug test.

Modified scope to always query a fresh list of variables since they may change on each single debugging step.

[GR-2798] The rbdiag tool exists with a non-zero status if a cast-pipeline related warning is issued during validation of a builtin.

The rbdiag tool exists with a non-zero status if a cast-pipeline related warning is issued during validation of a builtin