[DOCS] Test clicking on snippets links on docs pages

[bantic]

I noticed that one of the docs demos on the "Sorting" page was throwing an error when its 'component.js' snippet was clicked.

This adds a test to click all the snippets on all the docs pages, to keep them from going out of sync.

[bantic]

You can see the issue at the current live deployed docs.

• https://opensource.addepar.com/ember-table/docs/guides/header/fixed-columns#dynamic-fixed-columns
• Click "component.js" snippet label for the last demo ("Dynamic Fixed Columns")
• Error in console, no snippet shown

This PR fixes that, and a similar one on the "Sorting" docs page

[mixonic]

Good hunting 👍