Fix pvCanFollow usage in Conway and improve clarity in Shelley

[lehins]

Description

Fix wrong usage of pvCanFollow in Conway: fix #3901 and fix #3873
This problem happened because there was no documentation on pvCanFollow and names for bindings where totally useless. This proves my belief even further that ticks are not very useful for bindings.

Besides the bug fix this PR also includes:

• Make pvCanFollow match the spec and remove the SNothing wrapper
  around the newly proposed ProtVer
• Reduce duplication by adding hasLegalProtVerUpdate
• Add helper functions failOnJust, failOnNonEmpty, failureOnJust,
  failureOnNonEmpty to small-steps, which allow us to lazily get the
  offending value, without forcing the validation, when validation is
  turned off.
  cardano-ledger-alonzo-test-1.1.2.8 has not been released yet, so the
  version bump in Change 4 PParam fields from EpochNo to EpochInterval #3876 was incorrect

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• When applicable, versions are updated in .cabal and CHANGELOG.md files according to the
  versioning process.
• The version bounds in .cabal files for all affected packages are updated. If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• All visible changes are prepended to the latest section of a CHANGELOG.md for the affected packages. New section is never added with the code changes. (See RELEASING.md)
• Code is formatted with fourmolu (use scripts/fourmolize.sh)
• Cabal files are formatted (use scripts/cabal-format.sh)
• hie.yaml has been updated (use scripts/gen-hie.sh)
• Self-reviewed the diff

[teodanciu]

This is great, I love that the dangerous parts (which hold the risk of getting the arguments reversed) are contained in the higher level hasLegalProtVerUpdate and legalProtVer

Looks good to me.