Linux OSS CI use cmake built gtest (#3609)

Summary:
We are deprecating buck2 support in OSS. Migrate unit tests to cmake and run them in CI.

Pull Request resolved: https://github.com/pytorch/executorch/pull/3609

Test Plan: CI https://github.com/pytorch/executorch/actions/runs/9198444538/job/25301231796?pr=3609

Reviewed By: huydhn

Differential Revision: D57693481

Pulled By: kirklandsign

fbshipit-source-id: 4d31f07695d2162a58cd6267029ecfbe76b03cbe