Add from_single_file() support for Ideogram4 and Krea2 transformers

[buffett0323]

What does this PR do?

Adds from_single_file() support for Ideogram4Transformer2DModel and
Krea2Transformer2DModel.

Fixes #14122

Before submitting

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• Was this discussed/approved via a GitHub issue or the forum? Please add a link to it if that's the case.
  • Issue: from_single_file() support missing/incomplete for Ideogram4 and Krea2 transformers #14122
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?
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Who can review?

@sayakpaul @yiyixuxu @DN6