Pass DocumentClassConstPtr arguments by const reference

Pass DocumentClassConstPtr arguments by const reference

This arguments are shared_ptr objects, so they are not expensive to
copy. However, it makes sense to pass such pointers by const reference
when they are just intended for reading.

Some reading about this issue is here:
https://www.internalpointers.com/post/move-smart-pointers-and-out-functions-modern-c

Fixes some Coverity scan defects.