MethodMeta API to query of backends number and names

[shoumikhin]

Add a way to learn which backends are used for a particular Method

[pytorch-bot]

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[shoumikhin]

@pytorchbot label "topic: not user facing"

[mergennachin]

Hi @shoumikhin,

There's already very similar API added in #8520 and #8738

Do we need all these similar APIs - please add more context in the PR summary.

We should consolidate them and disambiguiate which ones to use.

Also the "topic: not user facing" is not appropriate -- since this is a user facing API addition.

Cc @cccclai @tarun292 , @larryliu0820 , @JacobSzwejbka

[shoumikhin]

@mergennachin these apis are to query MethodMeta for the backends used for a concrete Method. I believe the apis introduced by @cccclai are to fetch all the backends registered at runtime, regardless of a particular Program or Method.

[JacobSzwejbka]

I think the query on a single model is a reasonable addition, I agree it should have public api release notes.

I can imagine this being used once we have some support for device or for backend options

[tarun292]

@shoumikhin yep i think when you add the api release notes for this also please add when a user should use which API. Although it's reasonably clear to us, for new users i don't think it's very clear.

[cccclai]

This one seems helpful. The APIs I added is for the registered backend, but not the backend required from the models