Add keyboard option to carousel

Also adds unit tests for keyboard events.

Fixes #14468.

docs/_includes/js/carousel.html

@@ -178,6 +178,12 @@ $('.carousel').carousel()
          <td>true</td>
          <td>Whether the carousel should cycle continuously or have hard stops.</td>
        </tr>
+       <tr>
+         <td>keyboard</td>
+         <td>boolean</td>
+         <td>true</td>
+         <td>Whether the carousel should react to keyboard events.</td>
+       </tr>
       </tbody>
     </table>
   </div><!-- /.table-responsive -->