optimize_for_mobile: bring packed params to root module (#42740)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42740
Adds a pass to hoist conv packed params to root module.
The benefit is that if there is nothing else in the conv module,
subsequent passes will delete it, which will reduce module size.
For context, freezing does not handle this because conv packed
params is a custom object.
Test Plan:
```
PYTORCH_JIT_LOG_LEVEL=">hoist_conv_packed_params.cpp" python test/test_mobile_optimizer.py TestOptimizer.test_hoist_conv_packed_params
```
Imported from OSS
Reviewed By: kimishpatel
Differential Revision: D23005961
fbshipit-source-id: 31ab1f5c42a627cb74629566483cdc91f3770a94
