Added Type Hints for modeling_tf_encoder_decoder.py
# What does this PR do?

This pull request adds type hints for modeling_tf_encoder_decoder.py as outlined in Issue #16059 while not being on my main branch

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [x] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

@Rocketknight1 
@Rocketknight1 I think this is ready, though I am getting an odd error saying "module 'tensorflow' has no attribute 'tensor'" which  I am not sure how to resolve. Thanks and let me know if there is anything I need to fix! <|||||>@Batese2001 The issue was that one of your hints was `tf.tensor` instead of `tf.Tensor` - it was case-sensitive! I just changed it there, let's see if that fixes the tests. Note that because I made the change in the PR branch, you should `pull` those changes before committing/pushing any further updates, or you might get a branch conflict.<|||||>_The documentation is not available anymore as the PR was closed or merged._<|||||>Tests look good - that Torch error is totally unrelated to this PR. Are you happy for me to merge the PR at this point?<|||||>Wonderful! If you think it is ready, then I am all for merging! Thank you for your help
<|||||>Merged, and thanks for your help!