Blender Git Loki

DwM: optimize mesh batch conversion

- Replace GWN_vertbuf_attr_set with Gwn_VertBufRaw & GWN_vertbuf_raw_step
to avoid intermediate copy.
- Avoid extra conversion step with: float[3] -> short[3] -> Gwn_PackedNormal.
We can skip the short[3].

Gives approx 6% speedup here.