code: Symbol resolveUnaryOperator(DiagnosticPosition pos, JCTree.Tag optag, Env<AttrContext> env, Type arg) {
          return resolveOperator(pos, optag, env, List.of(arg));
      }
docs: Resolve operator.
  @param pos       The position to use for error reporting.
  @param optag     The tag of the operation tree.
  @param env       The environment current at the operation.
  @param arg       The type of the operand.