Add the NHS polyfills

We should add the NHS polyfills, else components will break in IE11.
This is part of the instructions for setting up the NHS frontend but
this had been missed until now.

https://github.com/nhsuk/nhsuk-frontend/blob/master/docs/installation/installing-with-npm.md#option-2-import-javascript-using-modules

Author: benjimarshall

ntbs-service/wwwroot/source/app.ts

@@ -12,6 +12,7 @@ import * as Sentry from '@sentry/browser';
 import * as SentryIntegrations from '@sentry/integrations';
 // @ts-ignore
 import Details from '../../node_modules/nhsuk-frontend/packages/components/details/details';
+import '../../node_modules/nhsuk-frontend/packages/polyfills';
 import VueAccessibleModal from 'vue-accessible-modal'
 import cssVars from 'css-vars-ponyfill';
 // Components