Support more open-source models

[neuropilot-captain]

Summary

• This PR adds support for 5 more open-source models: dcgan, wav2letter, vit_b_16, mobilebert, emformer_rnnt
• Update model export script

cc @cccclai @cbilgin

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/10463

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❌ 3 New Failures, 1 Unrelated Failure

As of commit b28672a with merge base a325c56 ():

NEW FAILURES - The following jobs have failed:

• Build documentation / check-urls (gh)
  Process completed with exit code 1.
• Check Labels / Check labels (gh)
  RuntimeError: Error checking labels: PR does not have required labels
• Lint / lintrunner / linux-job (gh)
  >>> Lint for examples/mediatek/model_export_scripts/wav2letter.py:

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / test-llava-runner-linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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[github-actions]

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[neuropilot-captain]

@pytorchbot label "partner: mediatek"

[pytorch-bot]

Didn't find following labels among repository labels: release note: Add 5 open-source model export scripts for MediaTek backend

[neuropilot-captain]

@pytorchbot label "partner: mediatek"