[activation checkpoint][dynamo] Wrap AC into Tag based higher order op (#102935)
These are the numbers with this PR
There are 3 main followups
* A naive partitioner gives better memory footprint than min-cut partitioner here. Currently, we are using min-cut partitioner. Waiting for @Chillee to discuss this further to either modify min-cut or add a naive partitioner.
* aot_eager is < 1x memory footprint. This is true even for non AC models. This could hide some inefficiency somewhere.
* inductor is giving very different memory numbers between AOT-traced-AC (duplicate early) vs this implementation. This leads to some inefficiency in inductor that we need to resolve.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/102935
Approved by: https://github.com/jansel
