Pass shared_ptr<> arguments by const reference

Pass shared_ptr<> arguments by const reference

These arguments 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.