I'm adding some asset APIs/types in C++ that the file-listing code would
use. I prefer porting this code to C++ over adding a C-API for the asset
code.
Includes some minor cleanups that shouldn't change behavior, like using
`MEM_new()`/`MEM_cnew()`, C++ style C-library includes,
`LISTBASE_FOREACH()`, removing unnecessary typedefs, etc.
cd84d3f3da