Refactoring FSDP. (#1586)
* refactor fsdp
* add trainer
* remove hidden layers
* update dockerfile
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Co-authored-by: Adam Louly <adamlouly@microsoft.com@orttrainingdev9.d32nl1ml4oruzj4qz3bqlggovf.px.internal.cloudapp.net>
Co-authored-by: JingyaHuang <huang_jingya@outlook.com>
