3/n Move Accelerator into strategy - move model_sharded_context()

[four4fish]

What does this PR do?

Move model_sharded_context() to strategies from Accelerator

Part of #10648

Does your PR introduce any breaking changes? If yes, please list them.

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[four4fish]

@ananthsub why this will be a breaking change?

[ananthsub]

@ananthsub why this will be a breaking change?

It's a breaking change since we're removing an API from the accelerator interface. If anyone implemented a custom accelerator which overrode model_sharded_context this PR would break that usage. I'm using the label more for posterity so its easy to identify all such breaking changes for the 1.6 release

[four4fish]

@ananthsub why this will be a breaking change?

It's a breaking change since we're removing an API from the accelerator interface. If anyone implemented a custom accelerator which overrode model_sharded_context this PR would break that usage. I'm using the label more for posterity so its easy to identify all such breaking changes for the 1.6 release

Yeah make sense! We don't have this override in internal fb or unit test, so didn't think about mark as breaking change. Will mark all move as breaking change then.