[quant][be] Move QAT tests to its own file (#108061)
Test Plan:
python test/test_quantization.py TestQuantizePT2EQAT
python test/test_quantization.py TestQuantizePT2EQATModels
Reviewers: jerryzh168, kimishpatel
Subscribers: jerryzh168, kimishpatel, supriyar
Pull Request resolved: https://github.com/pytorch/pytorch/pull/108061
Approved by: https://github.com/jerryzh168
