Return entities extracted from the raw input for TokenClassificationPipeline 
# 🚀 Feature request

Allow TokenClassificationPipeline to return entities extracted from the raw input.

## Motivation

Pretokenization (pre_tokenizer) can affect the "word" returned by the TokenClassificationPipeline. In this case `entity["word"] != sentence[entity["start"]:entity["end"]]` (see  #15785):

```python
from transformers import AutoTokenizer, AutoModelForTokenClassification, pipeline

MODEL_NAME = "elastic/distilbert-base-uncased-finetuned-conll03-english"
sentence = "My name is Clara and I live in Berkeley, California."

model = AutoModelForTokenClassification.from_pretrained(MODEL_NAME)
tokenizer = AutoTokenizer.from_pretrained(MODEL_NAME)

pipe = pipeline("token-classification", model=model, tokenizer=tokenizer, aggregation_strategy="simple")
entities = pipe(sentence)

print([(sentence[entity["start"]:entity["end"]], entity["word"]) for entity in entities])
# [('Clara', 'clara'), ('Berkeley', 'berkeley'), ('California', 'california')]
```
The pipeline should optionally return entities extracted from the input `sentence[entity["start"]:entity["end"]]`

## Who can contribute
@Narsil @LysandreJik 
I am in favor of adding a new key `text` for this.

- That does not break BC
- `text` is already used in other places (like `ASR Pipeline`)

The reason to add this is for users that might not be easily able to capture from the original sentence:

```python
from i, tokens in enumerate(pipe(dataset)):
    ...
    # logic
    sentence = dataset[i]
    ... 
```
Now that code works only if the dataset is deterministic, in the case that is it not (like reading from a queue in various readers), then it's a bit more cumbersome to do. Making it easy is something I think is a good idea.
<|||||>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.<|||||>bumped into this while looking for a similar issue ("f-16" is returned as "f - 16"). 
I couldn't find this option, is there any plan to include it?