Add WPT tests for hyperlink auditing privacy features

[ChrisC]

These would be testing primarily for the implementation of the ping attribute...

Originally filed by @npdoty in the main interop repo:
web-platform-tests/interop#584

[johannhof]

To quote from that issue:

Hyperlink auditing and the ping attribute have been justified by the requirement for privacy-focused features, both end user transparency (showing the user who will be notified when they click on the link) and end user control (letting users turn off these extra notification requests).

Unfortunately I don't think either of these is something that WPTs can technically test today, nor are conceptually meant to test.

[ChrisC]

I see that @npdoty did suggest the idea of writing manual tests for this behavior in the wpt repo:

• missing test for hyperlink auditing transparency wpt#42690
• missing test for hyperlink auditing user control wpt#42691

Perhaps we can decide at the next meeting whether or not writing manual tests are desirable, or if there's some other way to test that makes sense within the overall aims of WPT.