Add mask2former fp16 support
# What does this PR do?

Add float16 support to mask2former module and derivatives
Some operations and conversions were fixed in order to propagate the chosen user _dtype_ (ex: float32, float16) for input and embeddings. In this way, we can pass in fp16 tensors for inference.

## Who can review?

Similar PRs were reviewed by: @alaradirik, @amyeroberts, @LysandreJik

Hi @pedrohml, thanks for opening this PR! 

Could you add some tests for these models e.g. [like this one for ViT](https://github.com/huggingface/transformers/blob/dd9d45b6ecc0861847e21d461187711331a56138/tests/models/vit/test_modeling_vit.py#L320)<|||||>@amyeroberts thanks for review. do you mind to double check new changes ?<|||||>@pedrohml Thanks for iterating and adding some tests. The tests added should match the pattern of the ones [I linked to](https://github.com/huggingface/transformers/blob/dd9d45b6ecc0861847e21d461187711331a56138/tests/models/vit/test_modeling_vit.py#L320), rather than call integration tests that check logit values. There are two reasons for this: 
*  An independent test enables us to select as small as possible checkpoint / config to keep the CI runs as fast as possible
* It might not be robust, as we can expect some differences in the output logits. Out of interest, did you run the slow tests to confirm these pass? 
<|||||>> @pedrohml Thanks for iterating and adding some tests. The tests added should match the pattern of the ones [I linked to](https://github.com/huggingface/transformers/blob/dd9d45b6ecc0861847e21d461187711331a56138/tests/models/vit/test_modeling_vit.py#L320), rather than call integration tests that check logit values. There are two reasons for this:
> 
> * An independent test enables us to select as small as possible checkpoint / config to keep the CI runs as fast as possible
> * It might not be robust, as we can expect some differences in the output logits. Out of interest, did you run the slow tests to confirm these pass?

@amyeroberts 
Thanks for the heads up.. I managed to simplify the fp16 tests. Also, I was able to run tests locally using gpu to confirm all tests go green. This helped me to fix a mistake for oneformer workaround.
I appreciate if you can review again. Feel free to add something else.<|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_25093). All of your documentation changes will be reflected on that endpoint.