Casting to device inside of the Tokenizer
# 🚀 Feature request

I think it will make sense if the tokenizer.encode() and in particular, tokenizer.encode_plus() accepting a string as input, will also get "device" as an argument and cast the resulting tensors to the given device. Otherwise, in case of encode_plus(), one has to loop through the output dict and manually cast the created tensors.
You can just do:

```
from transformers import AutoTokenizer
import torch

tokenizer = AutoTokenizer.from_pretrained("bert-base-uncased")

device = "cuda" if torch.cuda.is_available() else "cpu"

text = "hello world"
encoding = tokenizer(text, return_tensors="pt").to(device)
```<|||||>Cool, thanks!