As part of StrringData -> std::string_view migration, a string copy was added to the WiredTigerSession::_openCursor implementation in order to create a guaranteed null termination on a std::string_view (formerly StringData) `url` argument.

This turns out to be too hot a path and caused BF-43741.

Interestingly, this `url` argument was a `const std::string&` until relatively recently, changed in SERVER-109350.

We need a null-terminated string in the first place because WT uses const char* strings. This should be investigated or the server will forever have these copies every time it communicates with WT.