R1:d1eda610fac6

Identify builtin files and give them open policies

Summary:
Fixes T7379. Currently, builtin files generate with a "users" view policy even if an install is public.

Because these files TTL after 7 days, there's no migration here. Installs won't see the fix actually happen for up to 7 days after updating, though.

Test Plan:
- Deleted a builtin.
- Loaded projects page to regenerate it.
- Saw new builtin had most open policy and was marked as a builtin.

Reviewers: btrahan

Reviewed By: btrahan…