Extend the testing of tokenizers that just have a legacy version
# 🚀 Feature request

For the moment, only tokenizers that have a rust version use the tests in `test_tokenization_common.py` file that use the `self.tokenizers_list` attribute that stores a (eventually some) model name stored on the hub.

As mentioned by @LysandreJik in this [discussion](https://github.com/huggingface/transformers/pull/11810#discussion_r643083834_), it might be interesting not to limit this tests for tokenizers that have a rust version. Indeed, some tests that use `self.tokenizers_list` do not compare the behavior of the legacy tokenizer and the rust tokenizer but only test their correct functioning. Moreover, other tests which use the `self.tokenizers_list` attribute, test a behavior of the rust version whereas one could expect the same behavior of the legacy version.

<!-- A clear and concise description of the feature proposal.
     Please provide a link to the paper and code in case they exist. -->

## Motivation

This would allow to test rust only and legacy only tokenizers in an (almost) equivalent way.

<!-- Please outline the motivation for the proposal. Is your feature request
     related to a problem? e.g., I'm always frustrated when [...]. If this is related
     to another GitHub issue, please link here too. -->

## Your contribution

I started working on it but some tests do not pass as is on legacy versions.

<!-- Is there any way that you could help, e.g. by submitting a PR?
     Make sure to read the CONTRIBUTING.MD readme:
     https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md -->
     
cc @LysandreJik , @sgugger 

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/master/CONTRIBUTING.md) are likely to be ignored.