Add pass to replace some ops with channels last variants. (#20788)

### Summary
Add a transformation pass to replace some operators with their channels
last variant. Currently only `convolution` and `avg_pool2d` are
implemented, as those are the only operators with a channels last
variant. In the future, the pass can be easily extended to support more
operators.

### Test plan
Tested by `pytest
backends/transforms/test/test_replace_ops_with_channels_last_variants.py`.