Make lexer tests runable again

I would like to look into some issues related to the model lexer  #15883.

I stumbled upon 2 minor problems when I tried running the lexer tests:

* antlr did not put the generated files in the correct directory
* grammer/verify.rs did not work with the most recent version of rust

With these changes (and setting CLASSPATH=/usr/share/java/antlr-4.4-complete.jar:$CLASSPATH) I was able to execute the tests.

Note that I just fixed the syntax errors and added `None` as 2. argument of `Literal`. I am not sure if this is correct however. I still have to take a closer look at what verify.rs actually does. Are there any helpful pointers?