Support stacks installation strategy and metadata #892
Description
Stack uses a different strategy to figure out platform and bindists:
- https://github.com/commercialhaskell/stackage-content/blob/master/stack/stack-setup-2.yaml
- https://github.com/commercialhaskell/stack/blob/5c7585001e8cc59f6d27e4e64002d0ac8e6af3c7/src/Stack/Setup.hs#L1616
This might make ghcup more useful for stack users who wish to retain the current behavior and may also pave the way for: #719