[mason] Migrate mason to its own repository

[arezaii]

Summary

Mason is currently a folder inside the Chapel repository. This makes it difficult to release updates to mason independently of the Chapel language. Other package managers/build tools are often included with their respective language, but have their own repository (e.g. rust+cargo). I have seen mention of an independent mason repository in older issues, (see https://github.com/chapel-lang/chapel/pull/16035#issuecomment-663222727, and https://github.com/chapel-lang/chapel/issues/7106), so I know this has at least been mentioned before, but I don't see much discussion about it.

This issue is to track the discussion of what it would take to move mason and identify potential problems with the end result.

Vision

1. create a mason repository, maybe chapel-lang/mason
2. mason becomes a git submodule of Chapel
3. mason specific issues migrated to new mason repo
4. new mason issues created on mason repo

Benefits

• Faster bugfixes/enhancements to mason
• Separate mason issues from Chapel issues

Issues

• adds complexity to deal with submodule
• requires updates to makefiles
• requires updates to Chapel CI and test configurations
• mason relies on Chapel's test framework
• others? (please comment)

[bradcray]

FWIW, I think the last time we discussed this, we felt as though the right time to do it would be when mason was sufficiently mature and in-use (by users as well as us) that it warranted the additional overheads that would be incurred by giving it its own release cycle and process. In the meantime, it felt prudent to keep it bundled with everything else. So I don't think there were any objections to this in principle.