Include license file in built distributions (#27783)
### Description
<!-- Describe your changes. -->
Add explicit license_files to Python package build metadata so
wheels/sdists expose standard License-File entries.
### 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. -->
Downstream compliance tooling may fail to discover license text when
only SPDX/classifier metadata is present and License-File fields are
missing, even if license files are included in the wheel.
