Support type-checking without compiling

[mpilgrem]

Some Haskell users seek workflows where they can type-check without bearing the 'cost' of compiling. See, for example:

• https://discourse.haskell.org/t/the-fastest-way-to-feed-ghc-type-errors-to-llm/13827
• https://discourse.haskell.org/t/how-to-achieve-anything-like-cabal-typecheck/11214

There is a related 2013 issue in the Cabal project:

• Explicitly support building with -fno-code haskell/cabal#1176

GHC provides the underlying functionality:

• https://downloads.haskell.org/ghc/latest/docs/users_guide/phases.html#ghc-flag-fno-code

I think the ideal would be a --[no-]code flag for stack build (enabled by default).