Update opaque-keys library to use block_id for html_id for new keys.

Catch more places where get_children was giving us version aware references.
LMS-11237

oh, and added a bulk ops call so use ?w=1

@cpennington @nasthagiri 
Is this the only place that BlockUsageLocators need to have special handling? It seems like this if should be factored out into a shared method in case others need to do the same thing. I think it would make it easier to read this method too, even if it isn't reused currently.