Migrate spec/javascripts/frequent_items/ to Jest

The following frontend tests should be migrated to Jest (&895 (closed)):

• spec/javascripts/frequent_items/components/app_spec.js !32498 (merged)
• spec/javascripts/frequent_items/components/frequent_items_search_input_spec.js !26114 (merged)
• spec/javascripts/frequent_items/components/frequent_items_list_spec.js !26114 (merged)
• spec/javascripts/frequent_items/components/frequent_items_list_item_spec.js !26114 (merged)
• spec/javascripts/frequent_items/store/actions_spec.js !32498 (merged)
• spec/javascripts/frequent_items/store/mutations_spec.js !32498 (merged)
• spec/javascripts/frequent_items/mock_data.js !32498 (merged)
• spec/javascripts/frequent_items/utils_spec.js !32498 (merged)