[Hardware] Add processor inputs to platform validation

[joerunde]

A followup to #16291

This moves the current_platform.validate_request call to after input preprocessing happens, so that the ProcessorInputs can also be passed to the platform. This will ensure the platform plugins have access to the tokenized prompt and multimodal data for validation as well.

This is a slightly api breaking change since implementations that don't accept the processed_inputs kwarg would break, but I've updated the tpu implementation here and vllm-ascend hasn't implemented it yet.

I'll wait for @NickLucche to test this on TPU this time before merging to make sure I didn't break it again

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[NickLucche]

LGTM, benchmark is running fine on TPU.

[njhill]

Thanks @joerunde