Created by: wojtuss

This is the core of the second version of INT8 quantization, C-API based only. Passes with quantization and optimizations are to be submitted in separate PRs shortly.

The code is an updated version of https://github.com/PaddlePaddle/Paddle/pull/15834. It also contains updated version of https://github.com/PaddlePaddle/Paddle/pull/15472.

test=develop