Serialize all ObjectScripts

This was left off in the confusion of the scripts-on-multiple-queues
merge which ran in parallel to the serializer merge.

Partially resolves #29949; note that it does not address the case of
ObjectScrips when in a non-clone context.
Ensure that we call _BuildTableAttributes on ObjectScrip

As noted in ec5943dd7, we have to do this so _ClassAccessible works
properly in the importer.  Now that we're serializing RT::ObjectScrip,
we have to be sure to build attributes on it.
Merge branch '4.2/serializer-objectscrips' into 4.2-trunk