Use upstream DTensor scatter strategy

[aditvenk]

Stacked PRs:

• Use upstream DTensor expand strategy #504
• Use upstream DTensor reshape strategy #503
• ->Use upstream DTensor scatter strategy #502
• Use upstream DTensor convolution backward strategy #501
• Use upstream DTensor convolution strategy #500
• Use upstream DTensor layer norm backward strategy #499
• Use upstream DTensor layer norm strategy #498
• Use upstream DTensor select scatter strategy #497
• Use upstream DTensor diagonal scatter strategy #496
• Use upstream DTensor convert strategy #495
• Use upstream DTensor constant pad strategy #494
• Use upstream DTensor index strategy #493
• Use upstream DTensor transpose strategy #492
• Use upstream DTensor reduction strategy #491
• Make AC recompute test topology-robust #490

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Use upstream DTensor scatter strategy

PyTorch now provides a scatter.src strategy that preserves AutoParallel's local sharding cases and also validates src shape compatibility, so the local scatter rule can be removed.

Authored with Claude.

[fmassa]

LGTM, thanks!

[aditvenk]

closing in favor of #505