Extract setting up ec2 linux and checkout to be composite actions (#80462)
Step 1 to gradually change our generated workflow scripts to be more compatible with reusable workflows.
This PR extracts three pieces of functionality into composite actions:
- Checking out the branch
- Setting up EC2 linux
- Building the linux binary
It also regenerates the workflows to use these new composite actions
This is not a complete list of things we'd like to extract. Keeping this PR small to get early feedback
Pull Request resolved: https://github.com/pytorch/pytorch/pull/80462
Approved by: https://github.com/seemethere
