fix(vue-instantsearch): Use getDefaultSlots in Highlighter.vue

Ensure that it works with Vue 3 and @vue/compat during a Vue 2 to 3
migration

packages/vue-instantsearch/src/components/Highlighter.vue

@@ -15,7 +15,7 @@ import { parseAlgoliaHit } from '../util/parseAlgoliaHit';
 import { getDefaultSlot, renderCompat, isVue3 } from '../util/vue-compat';
 
 const TextNode = isVue3
-  ? (props, context) => context.slots.default()
+  ? (props, context) => getDefaultSlot(context)
   : {
       render: renderCompat(function () {
         return getDefaultSlot(this);