rename CrossAttention to MultiHeadAttention (#14201)
### Description
<!-- Describe your changes. -->
rename the CrossAttention to MultiheadAttention since this op can also
be used as self 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. -->
Co-authored-by: Ubuntu <wy@v100-2.0cdb2e52twzevn1i4fi45bylyg.jx.internal.cloudapp.net>
