make all 3 gemms in Float8Linear support configurability, not user facing

[vkuzo]

Stack from ghstack (oldest at bottom):

• -> #315

Summary:

This PR adds some plumbing for how to eventually make all 3 gemms in a linear fwd/bwd configurable:

1. add LinearMMConfig to Float8Tensor to tie together the three ScaledMMConfig objects, one per gemm
2. add GemmInputRole to Float8Tensor to specify how to pick the right config
3. plumb all of these throughout the codebase

Note that none of this is user facing, and there is no logic change. Planned follow-ups:

• a future PR will make the per-gemm behavior configurable in a user facing way, which will hook up to the objects introduced in this PR
• a future PR will update the naming from x/w/dL_dY to input/weight/grad_output throughout the codebase

Test Plan:

./test/test_everything.sh

Reviewers:

Subscribers:

Tasks:

Tags:

Differential Revision: D59973551

[vkuzo]

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[facebook-github-bot]

This pull request has been merged in pytorch-labs/float8_experimental@c58fb5d6ac768f2213e7f65123cfff779bef9d87.