Listeners should have visitErrorNode throw an exception by default

[incident-recipient]

It is possible to get a false positive if errorNodes are encountered. The default implementation is to do nothing. The user can implement an exception to be thrown manually, but I'm concerned that it will be easy to forget and lead to difficult to diagnose bugs.

I'm going to see if this can be built into the generated code ANTLR produces with its "tool" code.

[incident-recipient]

I was having difficulty getting tests in ANTLR to pass with my modifications, although I didn't have a dedicated amount of time to devote to the problem.

A stopgap solution might be to have PDSL log a severe error if it notices any nodes are error nodes.