Proposal: Disallow DOM Mutation event listeners

[bathos]

I would like to be able to declare a policy that forbids the legacy DOM mutation event listeners:

https://w3c.github.io/uievents/#legacy-mutationevent-events

The main reason for this is to prevent browser extensions from adding them because they cause perf to tank. I’m not entirely sure that the way extension realms are implemented in Chromium honors the document policy, though, so this may not actually help in the browsers where it’s a problem.