Make 'env' argument to Session const (#13362)
### Description
<!-- Describe your changes. -->
The Env argument does not need to be mutable to call the underlying C
API. Update the Ort::Session ctor to have a const Env.
All other changes are from clang-format running.
### 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. -->
Cleanup
