New Lint Rule: no unnammed token value

[bennypowers]

fails:

a {
  color: #ee0000;
}

passes:

a {
  color: var(--rh-color-accent-brand-on-light, #ee0000);
}

In cases where the value has only one associated token name, the rule can autofix from the failure case to the passing case. In other cases, the warning message will list the applicable token names (aliases).