Revert "refactor(shorthand_fields): remove translate_backwards in favor of replaced_with (#13604)"

[nowNick]

Summary

This partially reverts commit 11405e5. (not all changes were added back again)

translate_backwards was an udocumented experimental API that was created in order to generate API responses that were backwards compatible after plugin's schema field rename. It was later replaced by deprecation.replaced_with field in the schema. In the meantime it had been used by some custom plugins that rely on this field. Hence the reason why we need to bring it back - in order for those custom plugins to work.

Checklist

• The Pull Request has tests
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

KAG-6947

[samugi]

would it make sense to turn this check into an early return?

I meant to highlight:

if new_field_value and
      new_field_value ~= ngx.null and

[nowNick]

I'm not sure I quite follow what you mean 🤔 - could you give me an example of this early return?

[samugi]

I meant instead of doing a long condition for the if maybe do:

if not new_field_value or new_field_value == ngx.null then
  return true
end

just to make it a bit more readable. I haven't thoroughly checked if this is the right logic and I'm not sure if it's a good idea here, you're more familiar with the logic to make the best decision - feel free to disregard, it's an extra minor comment.