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 +10,30 @@
   /**
     * 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 = {}) {
+  $.fn.variantAutocomplete = function(options) {
     function extraParameters(term) {
-      if (typeof(options['searchParameters']) === 'function') {
-        return options['searchParameters'](term)
+      if (typeof(options) === 'object') {
+        if (typeof(options['searchParameters']) === 'function') {
+          return options['searchParameters'](term)
+        } else {
+          console.warn(
+            "Solidus deprecation: Passing an object of parameters to variantAutocomplete is deprecated. Instead, on the options object, please declare `searchParameters` as a function returning the parameters.\n\n",
+            "Deprecated usage:\n",
+            "$('#id').variantAutocomplete({\n",
+            "  suppliable_only: true\n",
+            "})",
+            "\n\nNew usage:\n",
+            "$('#id').variantAutocomplete({\n",
+            "  searchParameters: function (_selectSearchTerm) { return { suppliable_only: true  } }\n",
+            "})"
+          )
+        }
       }
 
       return {}