Improve violation reporting location for no-unused-placeholders

[bmish]

Fixes #276 (half of it).

Situation 1:

module.exports = {
  create(context) {
    context.report({
      node,
      message: 'hello world', // violation should not be reported here
      data: {
        bar: 'abc' // violation should be reported here on the unused placeholder property
      }
    });
  },
};

Situation 2 (even worse because the violation is not even reported inside the specific context.report() call):

module.exports = {
  meta: {
    messages: {
      foo: 'hello world', // violation should not be reported here
    }
  },
  create(context) {
    context.report({
      node,
      messageId: 'foo',
      data: {
        bar: 'abc' // violation should be reported here on the unused placeholder property
      }
    });
  },
};