docs: AnnotationInfo getImmutableAnnotation(Symbol sym, VisitorState state) {
      String nameStr = sym.flatName().toString();
      AnnotationInfo known = wellKnownMutability.getKnownImmutableClasses().get(nameStr);
      if (known != null) {
        return known;
      }
      return threadSafety.getInheritedAnnotation(sym, state);
    }