squash Improve variantAutocomplete to be more reusable

Make variantAutocomplete backwards compatible. Users can still pass an
object of parameters, null or nothing, if the former is done, a
console.warn deprecation warning is shown.

backend/app/assets/javascripts/spree/backend/variant_autocomplete.js

@@ -10,16 +10,20 @@
  /**
  * Make the element a select2 dropdown used for finding Variants. By default, the search term will be
  * passed to the defined Spree::Config.variant_search_class by the controller with its defined scope.
- * @param {Object} options Options
+ * @param {Object|undefined|null} options Options
  * @param {Function|undefined} options.searchParameters Returns a hash object for params to merge on the select2 ajax request
  * Accepts an argument of the select2 search term. To use Ransack, define
  * variant_search_term as a falsy value, and q as the Ransack query. Note,
  * you need to ensure that the attributes are allowed to be Ransacked.
  */
- $.fn.variantAutocomplete = function(options = {}) {
+ $.fn.variantAutocomplete = function(options) {
  function extraParameters(term) {
- if (typeof(options['searchParameters']) === 'function') {
- return options['searchParameters'](term)
+ if (typeof(options) === 'object') {
+ if (typeof(options['searchParameters']) === 'function') {
+ return options['searchParameters'](term)
+ } else {
+ console.warn("Solidus deprecation: Passing an object of parameters to variantAutocomplete is deprecated. Instead, on the options object, please declare `searchParameters` as a function returning the parameters.")
+ }
  }
 
  return {}