onnxruntime

Rename DecoderMaskedMHA to DecoderMaskedSelfAttn (#15166)

### Description
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As synced offline, rename this op and will create another op for mha
that supports both self and cross attention.

### Motivation and Context
<!-- - Why is this change required? What problem does it solve?
- If it fixes an open issue, please link to the issue here. -->

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Co-authored-by: Ubuntu <wy@v100-2.0cdb2e52twzevn1i4fi45bylyg.jx.internal.cloudapp.net>