[pruning][core][feature] Implement convert for pruner (#97545)
Summary:
This PR implements `BaseSparsifier.convert()`, which performs module swapping.
The modules and mappings will be merged in a future PR.
Test Plan:
`python test/test_ao_sparsity.py -- TestBaseSparsifier.test_convert`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97545
Approved by: https://github.com/jerryzh168
