function isUsingIterationVar(vIf) {
  return !!getVForUsingIterationVar(vIf)
}
Check whether the given `v-if` node is using the variable which is defined by the `v-for` directive.
@param {VDirective} vIf The `v-if` attribute node to check.
@returns {boolean} `true` if the `v-if` is using the variable which is defined by the `v-for` directive.