[Backend Tester] Add embedding tests

[GregoryComer]

Add tests for embedding and embedding_bag.

[GregoryComer]

Stack from ghstack (oldest at bottom):

• [Backend Tester] Add SNR validation #12924
• [Backend Tester] Add upsample tests #12856
• [Backend Tester] Add more pointwise op tests #12855
• [Backend Tester] Add pointwise op tests #12854
• [Backend Tester] Add reduction op tests #12853
• [Backend Tester] Add index_put and index_select tests #12852
• [Backend Tester] Add slice and reshape tests #12851
• [Backend Tester] Add permute, transpose, and masked_fill tests #12850
• -> [Backend Tester] Add embedding tests #12849

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/12849

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⏳ No Failures, 93 Pending

As of commit a265cca with merge base 964fee9 ():
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