clusterizer: Add C++ templated wrappers
clusterizer: Add C++ templated wrappers

It's now possible to build meshlets or cluster bounds from 16-bit index
buffers. Note that we still produce meshopt_Meshlet structure which has
32-bit vertex indices, but since this structure isn't intended for use
at runtime it should be trivial to repack the data later.

zeux/meshoptimizer,zeux/meshoptimizer,zeux/meshoptimizer