[DML EP] Attention Kernel bug fix (#13879)
### Description
- Use same data type as input for mask_index tensor which is used as DML
GEMM API's C parameter.
- Remove gsl header include as it is already gets included transitively.
### Motivation and Context
- Why is this change required? What problem does it solve?
Bug found in internal conformance testing.
- If it fixes an open issue, please link to the issue here.
N/A
