OpenVINO EP registration, LMEvaluator handles model with single logits

[jambayk]

Describe your changes

• OpenVINO EP requires openvino.dll to be on PATH. importing openvino package helps do that if it's not already on PATH since python doesn't seem to discover it automatically from the site-packages directory.
• LMEvaluator with ortgenai backend now handles models that only return the logits for the final token. Tasks such as hellaswag require logits for more than one last token.

Checklist before requesting a review

• Add unit tests for this change.
• Make sure all tests can pass.
• Update documents if necessary.
• Lint and apply fixes to your code by running lintrunner -a
• Is this a user-facing change? If yes, give a description of this change to be included in the release notes.

(Optional) Issue link