Add an IDL test set to the suite based on current document

[jimsch]

Note - I needed to comment out two lines. I don't know if this is an
error in the IDL in the document or something else.

[hoppipolla-critic-bot]

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[wpt-pr-bot]

Reviewers for this pull request are: @Ms2ger and @wafflespeanut.

[Ms2ger]

It might be nice to have this running in workers as well; you can look at FileAPI/idlharness.{idl, html, worker.js} for inspiration. Let me know if you'd rather not do that.

[jimsch]

Adding the same tests for workers makes sense. The pointer gave me the starting point. It may be that the documentation should be updated some time as it just talks about the html version and not the worker version.