Replace ScriptInterface::Call* with new ScriptFunction functions

Finishes work started in rP24969.
This removes the boost-CPP function wrappers entirely, in favour of pure templated code in FunctionWrapper.h
The Call* functions were already heavily templated, so there is nothing really new here. I just use tag dispatch to reduce the number of overloads slightly.

The new functions do not need the script interface, only the script request.

Differential Revision: https://code.wildfiregames.com/D3912