Currently the limit on nesting in BSON is not enforced on timeseries collections, as demonstrated in this branch https://github.com/10gen/mongo/tree/binh.vo/experiment-nesting

This is both because we set DisableDocumentValidationForInternalOp in the timeseries write path, which causes fixDocumentsForInsert not to run validateDepth, and also because validateDepth itself does not recurse into BSONColumn data.