[xnnpack]lite-int][2/n] flatbuffer xnn_value schema (#87906)
serializer schema for xnnpack graphs
Differential Revision: [D39003170](https://our.internmc.facebook.com/intern/diff/D39003170/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87906
Approved by: https://github.com/digantdesai
