MLX delegate (part 1)

[metascroy]

Takes changes from #16718, but strips all ops (except addmm) and examples.

Part2 will add back ops, and part 3 will add back examples.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/17803

• 📄 Preview Python docs built from this PR

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❌ 1 New Failure, 9 Pending, 3 Unrelated Failures

As of commit 9fe0a67 with merge base e0e10cc ():

NEW FAILURE - The following job has failed:

• Cadence Build & Test / cpu-test / test-ops / test-ops (gh)
  examples/cadence/operators/test_g3_ops.py::ATenOpTestCases::test_g3_native_layer_norm_out_23

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• trunk / unittest-release / linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• trunk / unittest-release / macos / macos-job (gh) (detected as infra flaky with no log or failing log classifier)

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• trunk / test-huggingface-transformers-macos (bert|coreml_fp32_gpu|--quantize) / macos-job (gh) (trunk failure)

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[github-actions]

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[meta-codesync]

@metascroy has imported this pull request. If you are a Meta employee, you can view this in D94997043.

[manuelcandales]

add a note saying this is an experimental backend

[manuelcandales]

rebase to fix merge conflicts, and make sure CI is green

[manuelcandales]

stamping, let's make sure this doesn't go stale.

[digantdesai]

As Manual said about experimental in the README.md. Thanks Scott.