Build/Test/Repair multiple projects

[LecrisUT]

I am currently working on a project that has multiple sub-projects that have to be built with version sync between each other and would require the repair step to pull in the recently built (and repaired) wheels from the previous step. But getting that to works is really difficult, especially with the linux runners running in containers.

Instead what would help is for package_dir to accept a comma-separated list, and have all the steps run in groups, BEFORE_ALL -> BEFORE_BUILD -> BUILD_ALL_WHEELS -> REPAIR_ALL_WHEELS etc. It would also help to have the format variables more widely available in all the steps.