Export `isBlocked` alongside rrweb.record

[eoghanmurray]

This is a speculative PR as I'm wondering whether we shouldn't be leaving this file well enough alone until we migrate rrweb/record/index.ts on top of it.

Goal here is to expose isBlocked to the recording website.

There's also a question as to whether the entirity of the record.utils modulue should be exposed on the record side.