gltfpack: Filter out negligibly small weights
gltfpack: Filter out negligibly small weights

Instead of preserving all bone influences during sorting, we now discard
influences that, when encoded in a quantized 8-bit integer, result in
weight=0. Validator now warns about 0 influences associated with non-0
joints, and this fixes the warnings.

zeux/meshoptimizer,zeux/meshoptimizer,zeux/meshoptimizer