Mesh packer V1

[Crisspl]

Left TODO:

• [ ] triangle reordering - triangles sorted by area and "locality" in space (use 3d morton code for the latter)
• [ ] auto conversion into TRIANGLE_LIST
• [ ] fix bug of creating triangles with vertices of two different meshes. Usually happens when minAllocSize is set at low values
• [ ] handle per-instance attribs
• [ ] addr space shrink - IMO basically it should work like: first alloc everything, then create buffers with size just enough to fit allocated space, commit
• [ ] put asserts on things that shouldnt happen, everywhere (alloc, commit...)
• [ ] some more complex tests

[devshgraphicsprogramming]

use 3d morton code for the latter

I actually suggested kind-of truncating morton codes depending on triangle size, so we're doing both at the same time.