@Override
    public SourceVersion getSupportedSourceVersion() {
      return SourceVersion.latestSupported();
    }
Returns a "base type" for TypeSimplifier that does not contain any nested types. The point
being that every {@code TypeSimplifier} has a base type that the class being generated is going
to extend, and if that class has nested types they will be in scope, and therefore a possible
source of ambiguity.
value/src/test/java/com/google/auto/value/processor/TypeEncoderTest.java