16-bit indices are exposed in the API but left unimplemented, causing TDRs on client software

[NoahMercury]

trafficstars

TriangleMeshBuildInfo::index_type exists, but is ignored throughout the code base, and 32-bit indices are assumed instead. 16-bit indices are thus misinterpreted, causing out-of-bounds reads and TDR-ing unsuspecting client software.