Stack duplicates BuildTypes from Stackage

[Blaisorblade]

To fix #2487 I needed to adapt stack to fpco/stackage-curator@67484d7.

This requires adapting a copy of BuildPlan from https://github.com/fpco/stackage-curator/blob/67484d7d9e235c2a1ea725131390f19d0f13cde6/Stackage/Types.hs#L119. We also duplicate the Aeson instances.

Turns out we already miss build-tool-override, and I'm not going to fix that for #2487 to have a minimal fix before the release.

A possible solution would be to declare these shared types in an external package maybe?