Enable loading full optimizer checkpoints with FSDP

[leng-yue]

What does this PR do?

Making restoring optimizer states from full checkpoint possible, which is a supplement of #17623.

Before submitting

• Was this discussed/agreed via a GitHub issue? (not for typos and docs)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• Did you write any new necessary tests? (not for typos and docs)
• Did you verify new and existing tests pass locally with your changes?
• Did you list all the breaking changes introduced by this pull request?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or minor internal changes/refactors)

PR review

Anyone in the community is welcome to review the PR.
Before you start reviewing, make sure you have read the review guidelines. In short, see the following bullet-list:

Reviewer checklist

• Is this pull request ready for review? (if not, please submit in draft mode)
• Check that all items from Before submitting are resolved
• Make sure the title is self-explanatory and the description concisely explains the PR
• Add labels and milestones (and optionally projects) to the PR so it can be classified

[leng-yue]

Any update?

[awaelchli]

@leng-yue That's awesome, thank you so much for jumping on this so quickly! I have minor comments. Great work and thanks for extending the test!

[awaelchli]

Amazing!

[leng-yue]

I don't know why some tasks failed after I changed few lines, and there is no error message in azure pipelines...