CodeGen Tokenizer Deletes Newline Symbols
### System Info

- `transformers` version: 4.25.1
- Platform: Linux-5.15.0-58-generic-x86_64-with-glibc2.35
- Python version: 3.9.13
- Huggingface_hub version: 0.10.0
- PyTorch version (GPU?): 1.12.1.post201 (False)
- Tensorflow version (GPU?): not installed (NA)
- Flax version (CPU?/GPU?/TPU?): 0.6.3 (cpu)
- Jax version: 0.4.1
- JaxLib version: 0.4.1
- Using GPU in script?: No
- Using distributed or parallel set-up in script?: No

### Who can help?

@rooa @patrickvonplaten @patil-suraj

### Information

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

### Tasks

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

### Reproduction

The CodeGen tokenizer seems to remove the newline symbol in certain scenarios.
In particular, `decode(encode(text))` does not always equal the original `text`.
The following is the smallest example that reproduces the error but other text examples will have this issue as well.

```python
from transformers import CodeGenTokenizer

# other checkpoints in the CodeGen series have the same issue
tokenizer = CodeGenTokenizer.from_pretrained("Salesforce/codegen-350M-multi")

# new line (10), space (32), space (32)
text = "\n  "
print([ord(c) for c in text])
# output: [10, 32, 32]

encoded = tokenizer.encode(text)
print(encoded)
# output: [50286]

decoded = tokenizer.decode(encoded)
print([ord(c) for c in decoded])
# actual: [32, 32]
# expected: [10, 32, 32]
```

### Expected behavior

Expected: the decoded string is equal to the original string.
Actual: the decoded string is missing the leading new line symbol.
Hi, @hellodanylo this looks like the same issue described in issue #21120, where the tokenizer strips the whitespace and \n in front and at the end of the sentence. To overcome it use `tokenizer = AutoTokenizer.from_pretrained("Salesforce/codegen-350M-multi")`.<|||||>cc @ArthurZucker <|||||>@susnato thanks, using the fast tokenizer did solve this issue.

For future readers, you can get the fast tokenizer using either of the following ways:
```
tokenizer = AutoTokenizer.from_pretrained("Salesforce/codegen-350M-multi")
tokenizer = CodeGenTokenizerFast.from_pretrained("Salesforce/codegen-350M-multi")
```

If this bug is not specific to CodeGen tokenizer, then we can close this as duplicate of #21120?<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md) are likely to be ignored.