[Misc] Rename embedding classes to pooling

[DarkLight1337]

Part of #10674

• [Internal] VllmModelForEmbedding -> VllmModelForPooling
• [Internal] is_embedding_model -> is_pooling_model
• [Internal] EmbeddingModelRunner -> PoolingModelRunner
• [API] EmbeddingOutput -> PoolingOutput
• [API] EmbeddingRequestOutput -> PoolingRequestOutput

For API changes, the original name has been deprecated but remains accessible for now.

[github-actions]

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[youkaichao]

makes sense to me. we should add some docs to explain how embedding models are framed as pooling models. people are familiar with embedding, but not pooling.

[DarkLight1337]

Yeah, I'm planning to do that after splitting up the embedding task to more specific ones.