getMethodMetadata should contain used backend name

[phaiting]

Summary

This change added the metadata for used backend name for API getMethodMetadata()

Test plan

Run E2E test locally

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/14397

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❌ 4 New Failures, 3 Unrelated Failures

As of commit d9bcd14 with merge base 5fd66ee ():

NEW FAILURES - The following jobs have failed:

• Lint / android-java-format / linux-job (gh)
  RuntimeError: Command docker exec -t 88039c79304d16a242f7d2b0dd1487fd8d79e006cacde9a0eae11cbff74c7b83 /exec failed with exit code 1
• pull / test-llava-runner-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 0474ef65946eda469a7a929ddae36d09db0369444e82a7efed99e77594cc7f85 /exec failed with exit code 139
• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 46b181bb466bdbb28d87351113941aec46fd7d3231c35576e782c988a4bef569 /exec failed with exit code 1
• pull / unittest / macos / macos-job (gh)
  exir/tests/test_quant_fusion_pass.py::TestQuantFusionPass::test_embedding_torchao

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

• pull / test-custom-ops-linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• pull / test-moshi-linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• pull / test-qnn-models-linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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[cccclai]

@kirklandsign can you review?

[phaiting]

@pytorchbot label "release notes: none"

[cccclai]

Hey can you rebase?