[ghc-steering-committee] Mutable constructor fields

Hello, I am not sure what's the process for this, but I am really keen on Simon M's "Mutable constructor fields" proposal ( https://github.com/ghc-proposals/ghc-proposals/pull/8), so I'd like to propose that we adopt it. I'd be happy to volunteer time to work on the implementation too, if there's need for that. -Iavor