Filter the attributes that display on the json index view

This prevents data from displaying through the APIs even though it
wasn't clear that it would be displayed.
Fixes #1899

app/views/catalog/index.json.jbuilder

@@ -12,7 +12,16 @@ end
 json.data do
   json.array! @presenter.documents do |document|
     json.id document.id
-    json.attributes document
+    json.attributes do
+      doc_presenter = index_presenter(document)
+
+      index_fields(document).each do |field_name, field|
+        if should_render_index_field? document, field
+          json.set! field_name, doc_presenter.field_value(field_name)
+        end
+      end
+    end
+
     json.links do
       json.self polymorphic_url(url_for_document(document))
     end

spec/views/catalog/index.json.jbuilder_spec.rb

@@ -1,9 +1,18 @@
 # frozen_string_literal: true
 RSpec.describe "catalog/index.json" do
   let(:response) { instance_double(Blacklight::Solr::Response, documents: docs, prev_page: nil, next_page: 2, total_pages: 3) }
-  let(:docs) { [SolrDocument.new(id: '123', title_tsim: 'Book1'), SolrDocument.new(id: '456', title_tsim: 'Book2')] }
+  let(:docs) do
+     [
+       SolrDocument.new(id: '123', title_tsim: 'Book1', author_tsim: 'Julie'),
+       SolrDocument.new(id: '456', title_tsim: 'Book2', author_tsim: 'Rosie')
+     ]
+  end
   let(:facets) { double("facets") }
-  let(:config) { Blacklight::Configuration.new }
+  let(:config) do
+    Blacklight::Configuration.new do |config|
+      config.add_index_field 'title_tsim', label: 'Title:'
+    end
+  end
   let(:presenter) { Blacklight::JsonPresenter.new(response, facets, config) }
 
   let(:hash) do
@@ -44,12 +53,12 @@
     expect(hash).to include(data: [
       {
         id: '123',
-        attributes: { 'id' => '123', 'title_tsim' => 'Book1' },
+        attributes: { 'title_tsim' => 'Book1' },
         links: { self: 'http://test.host/catalog/123' }
       },
       {
         id: '456',
-        attributes: { 'id' => '456', 'title_tsim' => 'Book2' },
+        attributes: { 'title_tsim' => 'Book2' },
         links: { self: 'http://test.host/catalog/456' }
       },
     ])