(Created as a result of WT-10270)

The following B-Tree cursor calls are made from the RTS subsystem:

• wt_btcur_close
• wt_btcur_init
• wt_btcur_open

It would be worth reviewing the RTS code using these to see if a top-level cursor could be created and used instead.

There are also a number of dhandle_open calls that are made explicitly by RTS, moving to top-level cursor interfaces would hopefully remove the need for custom handling of data handles.

Some care is needed - RTS probably wants to aggressively close handles behind it, but it should be possible to annotate a handle with that semantic.