Update TF(Vision)EncoderDecoderModel PT/TF equivalence tests
# What does this PR do?

Make PT/TF equivalence tests for TF(Vision)EncoderDecoderModel aligned with the ones defined in `test_modeling_tf_common.py`:
- test all hidden states, attention outputs
- (and a minor bonus: consistent test names)
_The documentation is not available anymore as the PR was closed or merged._<|||||>> Would it be possible to move in the opposite direction, i.e. make the TFEncoderDecoder tests (or TFEncoderDecoderMixin itself) inherit from TFModelTesterMixin?

I also asked myself, and think it would be nice. Having something like `TFGenericEncoderDecoderModelTesterMixin` (or whatever  better names) and inheriting from there is good enough (see below). Regarding inheriting from `TFModelTesterMixin`, we have to skip some (or a lot of) tests that are not for encoder-decoder architectures, and requires some extra changes in `TFModelTesterMixin` to take into account encoder-decoder architectures. 

There is a previous related discussion:

- one from @patrickvonplaten (and more related to this discussion here): https://github.com/huggingface/transformers/pull/16280#issuecomment-1077449865
- from @sgugger https://github.com/huggingface/transformers/pull/16280#issuecomment-1077603150
- a thread: https://github.com/huggingface/transformers/pull/16280#discussion_r832036543

remark: the discussion regarding `is_encoder_decoder` there is (originally) more about Bart / T5 etc, not the `(Vision/Speech)EncoderDecoderModel`.<|||||>Okay I see the argument and I agree with it -- several composable mixins would be the way!

We may be able to carve out some tests from `TFModelTesterMixin` that are truly global, but streamlining `EncoderDecoder` tests seems more important 👍 I will be reviewing this PR soon with that in mind<|||||>@gante I also fixed `closed enough` in `tests/test_modeling_common.py` (thinking it is tiny that could be fixed in this PR too)