Add failing test for default-valued properties

[ryecroft]

@attr properties with a default value (specified using a getter method) incorrectly have their setter method called with an empty string after setting the property in the connectedCallback

This incorrect behaviour does not happen if:

• the property is in the html definition eg <initialize-attr-test has-foo='' />
• the property does not have a getter method supplying a default value

[primer-css]

👋 Hello and thanks for pinging us! This issue or PR has been added to our inbox and a Design Infrastructure first responder will review it soon.

• 🎨 If this is a PR that includes a visual change, please make sure to add screenshots in the description or deploy this code to a lab machine with instructions for how to test.
• ⏩ If this is a PR that includes changes to an interaction, please include a video recording in the description.
• ⚠️ If this is urgent, please visit us in #primer on Slack and tag the first responders listed in the channel topic.

[keithamus]

Thanks for filing this @ryecroft. I'll be looking into this soon hopefully!

[keithamus]

I'm going to merge this as I don't want the contribution to go unnoticed, but I don't think we'll get round to fixing this any time soon. Sorry.