Collect OSS GTest code coverage (#3734)

Summary:
Use LLVM coverage tool to collect coverage. We print it to log for now (https://productionresultssa7.blob.core.windows.net/actions-results/36302d2c-4406-4404-88c1-7b3e63331252/workflow-job-run-00b9f9ca-16b3-535c-a3c3-70113f2f2d24/logs/job/job-logs.txt?rsct=text%2Fplain&se=2024-05-28T21%3A48%3A03Z&sig=xgur5uWUJVMNRxkwkm%2BSeqCFFjsoYcnQKtFksKHcLHo%3D&sp=r&spr=https&sr=b&st=2024-05-28T21%3A37%3A58Z&sv=2021-12-02 and search for `Branches   Missed Branches     Cover`)

Later we can process the data in a separate workflow.

Pull Request resolved: https://github.com/pytorch/executorch/pull/3734

Reviewed By: huydhn

Differential Revision: D57792685

Pulled By: kirklandsign

fbshipit-source-id: 22942cdb012276d2541ff9fbff7f07014b87197b