Back out "Revert D25903846: [pytorch][PR] Structured kernel definition for upsample_nearest2d" (#50794)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50794
Original commit changeset: b4a7948088c0
There are some subtle extra tweaks on top of the original. I can unbundle them, but I've opted to keep it with the port because it's the easiest way to make sure the changes are exercised.
* There's a bugfix in the codegen to test if a dispatch key is structured *before* short circuiting because the dispatch key was missing in the table. This accounts for mixed structured-nonstructured situations where the dispatch table is present, but the relevant structured key isn't (because the dispatch table only exists to register, e.g., QuantizedCPU)
* Dispatch tables for functions which delegate to structured kernels don't have Math entries from generated for them.
* It's now illegal to specify a structured dispatch key in a delegated structured kernel (it will be ignored!) add is now fixed to follow this
* There are some extra sanity checks for NativeFunctions validation
* Finally, unlike the original PR, I switched the .vec variant of upsample_nearest2d to also be DefaultBackend, bringing it inline with upsample_nearest1d.
ghstack-source-id: 120038038
Test Plan:
```
buck test mode/dev //coreai/tiefenrausch:python_tests -- --exact 'coreai/tiefenrausch:python_tests - test_can_run_local_async_inference_cpu (coreai.tiefenrausch.tests.python_test.TiefenrauschPY)' --run-disabled
```
Reviewed By: ngimel
Differential Revision: D25962873
fbshipit-source-id: d29a9c97f15151db3066ae5efe7a0701e6dc05a3
