Revert unintended spec change re version number syntax

[hvr]

#5092 hghlighted an issue where a change in cabal 1.24 resulted in an unintended change to the cabal specification, specifically relaxing the version parser to unintentionally allow for denormalised version numbers (which are not isomorphic to NonEmpty Natural (where strictly speaking, Natural has an upper bound)).

Since there's little benefit to allow denormalisation, and it mostly causes subtly problems as e.g. it would violate an implicit assumption code may have head about version numbers round-tripping loss-free, causes trouble to older parsers, complicates the parser as it needs to support and keep track whether it encountered a denormalised version number, this may offer an opportunity for denial of service attacks and/or exploits (I've got more planned in this area, but I don't want to discuss this publicly before we don't have counter measures in place), but most importantly, this wasn't an intentional change to the spec to begin with, we shall consider this spec change to be a bug, and act accordingly.

Measures that were taken already

1. The 4 index entries on Hackage were revised (c.f. Invalid version number syntax for pre 1.24 spec versions haskell-infra/hackage-trustees#128); this means that clients which consume the 00-index.tar index will not be exposed to the original revisions which featured the invalid .cabal files.
2. cabal 2.2's parser was extended to detect denormalisation in order to have cabal check complain about invalid .cabal files
3. Hackage-server was retrofitted with an additional validation check which prevents new .cabal files with the invalid syntax to enter the index from now on.

Next steps

Since cabal > 1.24 currently happily tolerate denormal version numbers, and hackage now actively prevents from more invalid entries entering the package index, the next steps are not "urgent", and can be done whenever convenient:

• Add the 4 historic original .cabal revisions which have become part of the 01-index.tar index, as well as are included in the original .tar.gz to cabal's parser quirk-DB
• Remove support from the parsec parser for parsing (the invalid) denormal version numbers, turning them into ordinary parser failures (rather than cabal check warnings).