unit test with multiple op invocations (#19118)

unit test with multiple op invocations (#19118)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19118

A bug introduced by D14700576 reported by Yufei (fixed by D14778810 and D14785256) was not detected by our units tests.
This diff improves unit tests to catch such errors (with this diff and without D14778810, we can reproduce the bug Yufei reported).
This improvement also revealed a bug that affects the accuracy when we pre-pack weight and bias together and the pre-packed weight/bias are used by multiple nets. We were modifying the pre-packed bias in-place which was supposed to be constants.

Reviewed By: csummersea

Differential Revision: D14806077

fbshipit-source-id: aa9049c74b6ea98d21fbd097de306447a662a46d