[NNC] Adding API to distribute loops (#53865)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/53864
This PR adds the following APIs that perform loop distribution to `LoopNest`:
```
static std::vector<For*> distributeLoop(For* loop, const std::unordered_set<Stmt*>& pivots);
static std::vector<For*> distributeLoop(For* loop);
static std::vector<For*> distributeLoopOverInnerLoops(For* loop);
```
* The first method distributes the given loop over its body by splitting after every given pivot stmt.
* The second method distributes the given loop over every stmt in its body.
* The last method distributes the given loop over its body by splitting after every `For` stmt in its body.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53865
Reviewed By: mruberry
Differential Revision: D27075006
Pulled By: navahgar
fbshipit-source-id: 031746aad619fe84c109e78b53387535e7f77cef
