message: gltfpack: Merge index streams into one when compressing
  Now that we can use version=1 index codec, we can merge all index streams
  into one which is slightly more efficient in terms of binary size and
  JSON size, and faster to decode.
diff: @@ -3303,10 +3303,7 @@ size_t writeMeshIndices(std::vector<BufferView>& views, std::string& json_access
  std::string scratch;
  StreamFormat format = writeIndexStream(scratch, mesh.indices);
  - // note: we prefer to merge all index streams together; however, index codec currently doesn't handle concatenated index streams well and loses compression ratio
  - int variant = settings.compress ? -1 : 0;
  -
  - size_t view = getBufferView(views, BufferView::Kind_Index, variant, format.stride, settings.compress);
  + size_t view = getBufferView(views, BufferView::Kind_Index, 0, format.stride, settings.compress);
  size_t offset = views[view].data.size();
  views[view].data += scratch;
  @@ -4517,6 +4514,8 @@ int gltfpack(const char* input, const char* output, const Settings& settings)
  int main(int argc, char** argv)
  {
  + meshopt_encodeIndexVersion(1);
  +
  Settings settings = {};
  settings.pos_bits = 14;
  settings.tex_bits = 12;
  