Adapt BVH related code from RSX

[snake-biscuits]

Asked Amos in Northstar Discord about how they get physics models for generating R5R navmeshes

They pointed me to these sections of RSX:

src/game/rtech/assets/model.cpp:1933-1991

template <typename mstudiocollmodel_t, typename mstudiocollheader_t>
static bool ExportPhysicsModelBVH(const ModelAsset* const modelAsset, std::filesystem::path& exportPath)
{

src/game/rtech/assets/model.cpp:2144

case eModelExportSetting::MODEL_STL_RESPAWN_PHYSICS:
{
    // [amos]: the high detail bvh4 mesh seems encased in a mesh that is
    // more or less identical to the vphysics one. The polygon winding
    // order of the vphysics replica is however always inverted.
    if (modelAsset->version >= eMDLVersion::VERSION_12_1)
        return ExportPhysicsModelBVH<r5::mstudiocollmodel_v8_t, r5::mstudiocollheader_v12_t>(modelAsset, exportPath);
    else
        return ExportPhysicsModelBVH<r5::mstudiocollmodel_v8_t, r5::mstudiocollheader_v8_t>(modelAsset, exportPath);
}

they also gave me some notes on which lumps to pull vertex data
as well as positions being relative to MODELS origins
*coll trigger brush collision also came up

.rmdl uses the same BVH system as .bsps in r5
initially we thought this was how r2 physics work
since a respawn GDC talk on physics attributed the tech to r2

looks like some BVH node types are .bsp exclusive

better understanding of BVH would be massively beneficial to MRVN-Radiant