Workflow consolidation for GitHub actions

This PR implements the proposal in https://fb.quip.com/RcLZAOb9k0qI,
which calls for using GitHub's "normal" means of composition (composite
actions, reusable workflows) instead of codegen.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/74306

Approved by: https://github.com/janeyx99

tools/extract_scripts.py

@@ -63,6 +63,8 @@ def main() -> None:
 
         for job_name, job in workflow['jobs'].items():
             job_dir = out / p / job_name
+            if "steps" not in job:
+                continue
             steps = job['steps']
             index_chars = len(str(len(steps) - 1))
             for i, step in enumerate(steps, start=1):