[ci skip]

This commit reworks how GenericPackageDescription is parsed from
`[Field Position]` and pretty-printed to `Doc`.

This also fixes few issues:
- Fix #4697: `cabal format` doesn't output custom-setup stanza (nor
  foreign-lib stanzas)
- Fix #4719: `parse . pretty . parse = parse`  for all Hackage cabal files.
    - `parser-hackage-tests roundtrip` is the test program.

The handling of `license-file` and `license-files` is changed.
Now they behave the same.

Convenience for `stack build`.

The hackage-security dependency in stack.yaml (0.5.2.1) is incompatible
with what cabal-install requires (>=0.5.2.2). Bumping the version to that
lower bound resolves the issue.

The external zlib package is required to build the zlib Haskell
library. This change will not affect Stack-using developers who do not
have Nix integration enabled globally. This change will not affect
non-Stack-using developers at all.

I needed this when building cabal.exe for MinGHC (see:
https://github.com/fpco/minghc/issues/69). I thought others might find
this useful, especially for the use case of bootstrapping cabal
development.

I went the direction of no curation and explicit packages in the
extra-deps, as I thought that would make more sense for a project low on
the dependency chain, but this could certainly be tweaked to use LTS
Haskell or Stackage Nightly instead.