[V1][Kernel] Refactor the prefix_prefill kernel so that the caller no longer has to pass in the context lengths

[SageMoore]

This patch changes the prefix_prefill kernel so that it will calculate the context length using the query length and the sequence length, both of which are already passed in. This makes the kernel a bit more usable on V1 where we don't keep track of the context lengths tensor in the attention meta data.

[github-actions]

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