(Created as a result of WT-10270)

The RTS subsystem contains two direct calls for history store cursors:

• wt_curhs_search_near_after
• wt_curhs_search_near_before

Most cursor API calls go via a function pointer from a WT_CURSOR structure, these two bypass that because they aren't part of the standard cursor interface. We should introduce a new flag to cursors, that allows applications (in this case WiredTiger itself) to control search_near behaviour.

Some caution should be exercised here - this would be an addition to external-facing APIs, so extra thought is warranted about having a clean interface that could also be useful to non-WiredTiger users. (The MongoDB oplog is one such application, where it would be useful to give hints about the direction of a search_near.)