### Implementation of #151705
This PR introduces the initial implementation of native `tl.dot` support in Inductor, with the goal of generating Triton matmul kernels directly—without relying on predefined templates.
To avoid complexity and ease the review process, I plan to split this work into two phases as outlined in #151705:
1. **Basic support** (this PR)
2. **Lazy broadcasting** for optimal performance (future PR)
### Summary of This PR
This PR implements the basic functionality. It does **not** include lazy broadcasting, so the generated kernels may involve explicit `tl.reshape` and `tl.trans` operations before calling `tl.dot`, which introduces some overhead.
### Notable Changes
1. Adds a new config flag: `config.triton.enable_native_matmul`
2. Introduces a new `ops.dot` IR node in Inductor and lowers `aten.mm` and `aten.bmm` to it when native matmul is enabled
3. Enforces tililng suitable for matmul when the native matmul flag is enabled
4. Implements code generation for `ops.dot`
5. Adds Triton autotuning heuristics: for now, I’ve copied the configuration from the existing matmul templates. However, this may not be optimal—it currently takes a long time to tune, and I think there must be a better way to tackle this.
@eellison @jansel @PaulZhang12 @shunting314
Pull Request resolved: https://github.com/pytorch/pytorch/pull/157743
Approved by: https://github.com/jansel
