[core] deprecate torch_dtype and prefer dtype following transformers.

[sayakpaul]

Followups of #14162 and huggingface/huggingface.js#2280

[HuggingFaceDocBuilderDev]

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[DN6]

I would introduce a utility function here

def _resolve_dtype(dtype, torch_dtype):
    """Resolve the deprecated `torch_dtype` argument into `dtype`."""
    if torch_dtype is None:
        return dtype
    if dtype is not None:
        raise ValueError(
            "You have passed both `dtype` and `torch_dtype`. Please only pass `dtype`, `torch_dtype` is deprecated."
        )
    deprecate("torch_dtype", "1.0.0", _TORCH_DTYPE_DEPRECATION_MESSAGE)
    return torch_dtype

The call sites become simpler

# from_pretrained
torch_dtype = kwargs.pop("torch_dtype", None)
dtype = _resolve_dtype(kwargs.pop("dtype", None), torch_dtype)

# from_pipe
torch_dtype = kwargs.pop("torch_dtype", None)
dtype = _resolve_dtype(kwargs.pop("dtype", None), torch_dtype) or torch.float32

# modular_pipeline_utils.load
torch_dtype = kwargs.pop("torch_dtype", None)
if torch_dtype is not None:
    kwargs["dtype"] = _resolve_dtype(kwargs.get("dtype"), torch_dtype)