Add show-hide-content.js
Add show-hide-content.js

Related PR for the front end toolkit:
https://github.com/alphagov/govuk_frontend_toolkit/pull/305

Related PR for elements:
https://github.com/alphagov/govuk_elements/pull/287

alphagov/govuk_accessibility_sandbox,alphagov/govuk_accessibility_sandbox,alphagov/govuk_accessibility_sandbox