Update ViT for feature extraction, support elative positional embedding and layer scale

[SamitHuang]

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Motivation

Previous ViT mainly aimed at image classification, which is not convenient to extend for unsupervised learning or detection. This PR makes ViT more extendable.

Test Plan

python infer.py --model vit_b_32_224 --image two_cats.jpg

Related Issues and PRs

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[SamitHuang]

TODO: upload the checkpoints with the new param names

[SamitHuang]

TODO: upload the checkpoints with the new param names

done

[SamitHuang]

closed. Progress will be continued in https://github.com/mindspore-lab/mindcv/pull/707