Adds failing tests for the fast tokenizers
This ports some of the tests over that started failing on the AllenNLP side when the new fast tokenizers came out.

Note: These tests are failing right now. They will need updates to the fast transformers before this can be merged. Maybe it would be better to merge this branch into the branch where the tokenizers are being fixed?
I can't assign reviewers, but you asked me in #3058 to ping @LysandreJik and @mfuntowicz when I do this.<|||||>I added a test for the issue from #3088.<|||||>Added another test for #3091.<|||||>@dirkgr thanks for taking the time to include your tests into ours. 

It will definitively help making sure everything is working as expected on your side 👍 <|||||>This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
<|||||>This can be closed now, right?<|||||>This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
