Add support for partial rotary embeddings in Phi3 model

[garg-amit]

What does this PR do?

This PR adds support for partial rotary embeddings in the Phi3 model. Key changes include:

• Introducing the partial_rotary_factor parameter in Phi3Config to control the percentage of queries and keys using rotary embeddings.
• Modifying the apply_rotary_pos_emb function to accommodate partial rotary embeddings.
• Updating validation checks in Phi3Config to ensure the correct application of the rotary embedding dimensions.

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[Rocketknight1]

Hi @garg-amit, are there any trained models using this right now?

[garg-amit]

@Rocketknight1 Not at the moment, but I believe users will have more flexibility when experimenting with different rotary embeddings.
Note: This does not affect the current behavior.

[Rocketknight1]

Seems like a clean addition to the RoPE code that shouldn't have any backward compatibility effects to me! cc @ArthurZucker @Cyrilvallez for core maintainer review

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[ArthurZucker]

Okay, the change is quite minimal and not breaking. This is a bit against our philo, but we'll justify later! 🤗

[ykim362]

Thanks! Now, the Phi-4-mini is delivered. :) Justified!