Make Swin work with VisionEncoderDecoderModel
# What does this PR do?

This PR sets the `hidden_size` attribute of the config of Swin Transformer, allowing it to be used with the `VisionEncoderDecoderModel` framework.


It also adds an attribute_map to the config of Swin Transformer.

Fixes #15526 
_The documentation is not available anymore as the PR was closed or merged._