[Doctests] Make TFRoberta-like meaningfull 
# What does this PR do?

Similar to #16363, but for TF

I made sure the doctests run without failure, but 2 models currently use `from_pt=True` --> need to convert and upload the TF ckpts.

@patrickvonplaten 
_The documentation is not available anymore as the PR was closed or merged._<|||||>@patrickvonplaten I uploaded the TF checkpoints and removed `from_pt`.

~~I will need to check and apply Sylvain's suggestion in your PR to finalize this PR.~~

Ready for review :-)