Restrict parser to only accept !. Furthermore, we should only accept ! in the following places:

* A field declaration type (including a record component)
* A local variable declaration type (including a type pattern)
* A formal parameter type (including receiver parameters, but excluding variable arity parameters)
* An exception parameter type
* A method result type
* A cast type or an instanceof type
* The element type of an array creation expression (excluding multi-dimensional arrays)