This is the conventional way of dealing with unused arguments in C++,
since it works on all compilers.
Regex find and replace: `UNUSED\((\w+)\)` -> `/*$1*/`
Moves all `interface_region*` files to C++ except for the tooptip region
which is slightly more complicated. Also move a few other files as well.
This helps to simplify and speed up code, especially through the use
of better C++ data structures. This change builds on all platforms on
the buildbot.
