Separate out Package utilities & enforce better typing discipline

[isovector]

This PR moves the Utilities section out of Distribution.Server.Packages.Types and into Distribution.Server.Packages.Utils. It then adds:

+data MetadataRevision = MetadataRevision
+  { metaRevCabalFile :: CabalFileText
+  , metaRevInfo :: UploadInfo
+  }
+  deriving stock Show

-type UploadInfo = (UTCTime, UserId)
+data UploadInfo = UploadInfo
+  { uploadInfoTime :: UTCTime
+  , uploadInfoUser :: UserId
+  }
+  deriving stock Show

These new datatypes used to be anonymous tuples, and their new existence gives an easy-to-target API for the work in #1486. This PR is careful to not use the new MetadataRevision constructor anywhere, so that it can be trivially swapped out for a structure that can be pulled out of the database.

In addition, we keep OldUploadInfo around, since swapping it inside of the acid-state would be a breaking serialization change. Furthermore, all of the utility implementations are copied verbatim into Packages.Utils.Acid, since they're still required for *.State maintenance, and will diverge more dramatically in upcoming PRs.

This PR also changes the type of pkgDesc:

-pkgDesc :: PkgInfo -> GenericPackageDescription
+pkgDesc :: MetadataRevision -> GenericPackageDescription

which makes it clear that it is a function of a specific revision, rather than of the package-as-a-whole. This in turn revealed some bugs in the feed code, which was using the wrong dates. I will send a separate PR fixing those issues.