Fixing missing arguments for TransfoXL tokenizer when using TextGenerationPipeline
Author: TevenLeScao
Pull request: yes

As discussed with @LysandreJik and @mfuntowicz , `TextGenerationPipeline` gives imperfect results when using TransfoXL as the tokenizer lacks the `add_space_before_punct_symbol` argument. In order to fix this, this PR overrides `_parse_and_tokenize` for this pipeline in order to pass tokenizer arguments.

Comments:
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/5465?src=pr&el=h1) Report
> Merging [#5465](https://codecov.io/gh/huggingface/transformers/pull/5465?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/6726416e4a9780e7a92b5681e1446f15f7ef83d3&el=desc) will **decrease** coverage by `0.12%`.
> The diff coverage is `85.71%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/5465/graphs/tree.svg?width=650&height=150&src=pr&token=9qOlN6Hb1c)](https://codecov.io/gh/huggingface/transformers/pull/5465?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #5465      +/-   ##
==========================================
- Coverage   77.52%   77.40%   -0.13%     
==========================================
  Files         141      141              
  Lines       24610    24617       +7     
==========================================
- Hits        19079    19054      -25     
- Misses       5531     5563      +32     
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/5465?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/pipelines.py](https://codecov.io/gh/huggingface/transformers/pull/5465/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9waXBlbGluZXMucHk=) | `76.00% <85.71%> (+0.11%)` | :arrow_up: |
| [src/transformers/tokenization\_albert.py](https://codecov.io/gh/huggingface/transformers/pull/5465/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fYWxiZXJ0LnB5) | `28.84% <0.00%> (-58.66%)` | :arrow_down: |
| [src/transformers/generation\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5465/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9nZW5lcmF0aW9uX3V0aWxzLnB5) | `96.82% <0.00%> (-0.29%)` | :arrow_down: |
| [src/transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5465/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9maWxlX3V0aWxzLnB5) | `79.59% <0.00%> (+0.33%)` | :arrow_up: |
| [src/transformers/configuration\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/5465/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9jb25maWd1cmF0aW9uX3V0aWxzLnB5) | `96.40% <0.00%> (+0.71%)` | :arrow_up: |
| [src/transformers/tokenization\_auto.py](https://codecov.io/gh/huggingface/transformers/pull/5465/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25fYXV0by5weQ==) | `97.77% <0.00%> (+2.22%)` | :arrow_up: |
| [src/transformers/tokenization\_xlm\_roberta.py](https://codecov.io/gh/huggingface/transformers/pull/5465/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy90b2tlbml6YXRpb25feGxtX3JvYmVydGEucHk=) | `95.23% <0.00%> (+33.33%)` | :arrow_up: |

------

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> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/5465?src=pr&el=footer). Last update [6726416...25f8c86](https://codecov.io/gh/huggingface/transformers/pull/5465?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).