Consider recommending the usage of events instead of CSP reports for CSP WPTs

[mbrodesser-Igalia]

¹ mentions to check reports to determine whether CSPs prevented script from running. ¹ existed already in the year 2017, when securitypolicyviolation events weren't supported ² by all major browser engines.
Using such events seems simpler for some test scenarios.

Footnotes

1. https://searchfox.org/mozilla-central/rev/6050bf4eca89956c9d91bfd89fa59294ae32a689/testing/web-platform/tests/content-security-policy/README.html#29-30 ↩ ↩²

2. https://developer.mozilla.org/en-US/docs/Web/API/Element/securitypolicyviolation_event#browser_compatibility ↩