Fix Hpack #530 Make use of prettier Hpack error messages

[mpilgrem]

For the context to this pull request see Hpack issue #530, the Hpack PR #531 and the alternative Hpack PR #535 (on which this PR builds).

This PR is draft until such time as there is a released version of Hpack on which it relies.

[sol]

@mpilgrem I think the MacOS build error is likely possibly related to caching. I deleted the cache entry and re-initiated the build.

[sol]

Ok, so apparently it was the cache. I'm still not sure how exactly. But some observations:

• GitHub is currently migrating macos-latest from macos-11 to macos-12. This means that we might sometimes end up with one or the other.
• We key the cache over the file name (say stack.yaml) instead of over the content of the file (https://github.com/commercialhaskell/pantry/blob/master/.github/workflows/tests.yml#L46), or better even the content of the lock files. However, this should only affect cache efficiency, not correctness. (Note: If somebody were to look into this, then you probably also want to specify restore keys.)
• Initially I thought the issue is that we cache /.stack-work, something that you see e.g. in the docs of the caching action, but what I personally would refrain from doing. However, we don't do that already.

[mpilgrem]

Example output of Pantry (via Stack):

Duff package.yaml:

Error: [S-305]
Failed to generate a Cabal file using the Hpack library on file:
D:\Users\mike\Code\Haskell\boo\package.yaml

The error encountered was:

YAML parse exception at line 64, column 0,
while scanning a simple key:
could not find expected ':'

Duff defaults.yaml used by package.yaml:

Error: [S-305]
Failed to generate a Cabal file using the Hpack library on file:
D:\Users\mike\Code\Haskell\boo\package.yaml

The error encountered was:

In respect of an Hpack defaults file:
D:\Users\mike\Code\Haskell\boo\defaults.yaml:

YAML parse exception at line 3, column 0,
while scanning a simple key:
could not find expected ':'