[pruning][core][feature] Add in SaliencyPruner to pruner._experimental (#91814)
Summary:
This PR adds in SaliencyPruner, an implementation of L1 norm pruning for structured pruning, as well as additional tests for the SaliencyPruner
The README.md references this file but I forgot to add it in earlier when writing the tutorial.
Test Plan:
```
python test/test_ao_sparsity.py -- TestSaliencyPruner
```
Reviewers:
Subscribers:
Tasks:
Tags:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/91814
Approved by: https://github.com/jerryzh168
