[ExecuTorch] Add //examples/portable/executor_runner:executor_runner_opt (#9508)

This PR was created by the merge bot to help merge the original PR into
the main branch.
ghstack PR number: https://github.com/pytorch/executorch/pull/9291 by
@swolchok
^ Please use this as the source of truth for the PR details, comments,
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ghstack PR base:
https://github.com/pytorch/executorch/tree/gh/swolchok/367/base
ghstack PR head:
https://github.com/pytorch/executorch/tree/gh/swolchok/367/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/main
Merge bot PR head:
https://github.com/pytorch/executorch/tree/gh/swolchok/367/orig
@diff-train-skip-merge

Co-authored-by: Scott Wolchok <swolchok@meta.com>