update all tf.shape and tensor.shape to shape_list
We need to use the special method `shape_list` from `modeling_tf_utils` to be sure we can get TF 2.0 tensor shapes both in eager and non-eager mode.

This PR fixes this for all TF 2.0 models and templates.
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/1980?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@49a69d5`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `90.69%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/1980/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/1980?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master    #1980   +/-   ##
=========================================
  Coverage          ?   84.05%           
=========================================
  Files             ?      105           
  Lines             ?    15533           
  Branches          ?        0           
=========================================
  Hits              ?    13056           
  Misses            ?     2477           
  Partials          ?        0
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/1980?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [transformers/modeling\_tf\_transfo\_xl\_utilities.py](https://codecov.io/gh/huggingface/transformers/pull/1980/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3RmX3RyYW5zZm9feGxfdXRpbGl0aWVzLnB5) | `85.57% <100%> (ø)` | |
| [transformers/modeling\_tf\_ctrl.py](https://codecov.io/gh/huggingface/transformers/pull/1980/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3RmX2N0cmwucHk=) | `97.86% <100%> (ø)` | |
| [transformers/modeling\_tf\_transfo\_xl.py](https://codecov.io/gh/huggingface/transformers/pull/1980/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3RmX3RyYW5zZm9feGwucHk=) | `92.54% <100%> (ø)` | |
| [transformers/modeling\_tf\_distilbert.py](https://codecov.io/gh/huggingface/transformers/pull/1980/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3RmX2Rpc3RpbGJlcnQucHk=) | `98.66% <100%> (ø)` | |
| [transformers/modeling\_tf\_roberta.py](https://codecov.io/gh/huggingface/transformers/pull/1980/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3RmX3JvYmVydGEucHk=) | `90.43% <100%> (ø)` | |
| [transformers/modeling\_tf\_xlnet.py](https://codecov.io/gh/huggingface/transformers/pull/1980/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3RmX3hsbmV0LnB5) | `88.16% <100%> (ø)` | |
| [transformers/modeling\_tf\_gpt2.py](https://codecov.io/gh/huggingface/transformers/pull/1980/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3RmX2dwdDIucHk=) | `94.75% <100%> (ø)` | |
| [transformers/modeling\_tf\_openai.py](https://codecov.io/gh/huggingface/transformers/pull/1980/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3RmX29wZW5haS5weQ==) | `95.92% <100%> (ø)` | |
| [transformers/modeling\_tf\_albert.py](https://codecov.io/gh/huggingface/transformers/pull/1980/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3RmX2FsYmVydC5weQ==) | `85.26% <81.81%> (ø)` | |
| [transformers/modeling\_tf\_bert.py](https://codecov.io/gh/huggingface/transformers/pull/1980/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL21vZGVsaW5nX3RmX2JlcnQucHk=) | `96.31% <84.61%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/huggingface/transformers/pull/1980?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/1980?src=pr&el=footer). Last update [49a69d5...255516a](https://codecov.io/gh/huggingface/transformers/pull/1980?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>Very nice!