coreml: Add a few missing operators (#26462)
### Description
Adds `Elu`, `Exp` and `Softplus` to coreml.
### Motivation and Context
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- If it fixes an open issue, please link to the issue here. -->
We use them in LeelaChessZero.
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Co-authored-by: borg323 <borg323@users.noreply.github.com>
