Fix forward reference imports in DeBERTa configs
# What does this PR do?

#17617 introduced some imports that will create cyclical references, just for type hinting. This PR makes them only imported in a type checking block.
_The documentation is not available anymore as the PR was closed or merged._<|||||>FYI @JingyaHuang @michaelbenayoun I'll take a look at the slow test tomorrow :)