As a follow-on to WT-6722, for Skunkworks, I'm going to start a POC to use a different prefix than __wt for functions that are called in multiple files, but are only used within a single subsystem.

I'm going to do this on a per-directory/subsystem level, doing one at a time.

The intent is to increase visibility into what functions are used inter-subsystem versus intra-subsystem, but from multiple files. This ticket does not change any modularity of a subsystem. The intent is:

1. That all functions in a source file beginning with wti are only used or called by other files within that directory.
2. That all functions in a source file beginning with wti are used in at least two files within that directory.
3. That all functions in a source file beginning with wt_ are used somewhere outside of that directory. Typically it would be another directory but could be from some of the include/*_inline.h header files.