Changes to numerous ReportBody sub-classes has reduced IDL test coverage

[schenney-chromium]

The IDL changes committed in #53311 have many instances of things like:

interface CSPViolationReportBody : ReportBody becoming dictionary CSPViolationReportBody : ReportBody

The number of subtests in the related IDL WPT has dropped in response, now that there are no more tests for e.g. CSPViolationReportBody interfaces.

I would expect to see more tests somehow covering the new dictionary behavior. But there are no new tests. It seems very unlikely that all the browser have already implemented the changes, suggesting test coverage is indeed lacking.