

TITLE
Chinese parentheses can't be handled by fast tokenizer

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### Problem description

The chinese language has some special characters for parentheses: "（",  "）" (= parentheses with an integrated whitespace). Both characters aren't part of the XLMRoBERTa Tokenizer, neither the fast nor the "slow" one. Interestingly enough, it is possible to add these characters to the tokenizer vocabulary but only for the "slow"/non-fast tokenizer variant.

### System Info

```shell
Package            Version
------------------ ---------
certifi            2021.10.8
charset-normalizer 2.0.12
click              8.1.3
filelock           3.6.0
huggingface-hub    0.5.1
idna               3.3
joblib             1.1.0
numpy              1.22.3
packaging          21.3
pip                20.0.2
pkg-resources      0.0.0
pyparsing          3.0.8
PyYAML             6.0
regex              2022.4.24
requests           2.27.1
sacremoses         0.0.53
sentencepiece      0.1.96
setuptools         44.0.0
six                1.16.0
tokenizers         0.12.1
torch              1.11.0
tqdm               4.64.0
transformers       4.18.0
typing-extensions  4.2.0
urllib3            1.26.9
```


### Who can help?

@LysandreJik, @Sau

### Information

- [ ] The official example scripts
- [X] My own modified scripts

### Tasks

- [ ] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [X] My own task or dataset (give details below)

### Reproduction

### Code to reproduce

```python
import sentencepiece
import transformers
from transformers import AutoTokenizer

print("Transformers version:", transformers.__version__)
print("----------------")

special_chinese_parantheses = "（"
print(special_chinese_parantheses)

# "slow"
tokenizer = AutoTokenizer.from_pretrained("xlm-roberta-base", use_fast=False)
print(tokenizer.tokenize(special_chinese_parantheses))

tokenizer.add_tokens(special_chinese_parantheses)
print(tokenizer.tokenize(special_chinese_parantheses))
print("----------------")

# fast
tokenizer_fast = AutoTokenizer.from_pretrained("xlm-roberta-base", use_fast=True)
print(tokenizer_fast.tokenize(special_chinese_parantheses))

tokenizer_fast.add_tokens(special_chinese_parantheses)
print(tokenizer_fast.tokenize(special_chinese_parantheses))
```

### Output

```sh 
Transformers version: 4.18.0
----------------
（
['▁(']
['（']
----------------
['▁(']
['(']
```