Add new API KernelContext_GetScratchBuffer (#19809)
### Description
<!-- Describe your changes. -->
add new API KernelContext_GetScratchBuffer to get scratch buffer from
kernel context
### 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. -->
add new API KernelContext_GetScratchBuffer to get scratch buffer from
kernel context which will be used in ORT extension project for
GroupQueryAttention custom op
