Use the same emoji data on the frontend and backend (#4284)

* Use the same emoji data on the frontend and backend

* Move emoji.json to repository, add tests

This way you don't need to install node dependencies if you only
want to run Ruby code

spec/lib/emoji_spec.rb

@@ -0,0 +1,15 @@
+require 'rails_helper'
+
+RSpec.describe Emoji do
+  describe '#unicode' do
+    it 'returns a unicode for a shortcode' do
+      expect(Emoji.instance.unicode(':joy:')).to eq '😂'
+    end
+  end
+
+  describe '#names' do
+    it 'returns an array' do
+      expect(Emoji.instance.names).to be_an Array
+    end
+  end
+end