Avoid parse error for empty parameter list for annotations

[ujhelyiz]

When writing an annotation without parameters but with parentheses, a parse error is thrown, e.g.

@FunctionalDependency()
pattern a(b, c){
  Class(b);
  Class(c);
}

throws a mismatched input ')' expecting RULE_ID error. We should allow adding empty parentheses optionally, while still favoring the previous syntax.