refactor(router/atc): cleanup split routes and services

[bungle]

Summary

Just a slightly tighter code and reusing table.

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

This was originally proposed at #12901 for inclusion in #12875.

REBASE AND MERGE

[chronolaw]

This PR has almost the same logic as the original code, but it also introduces two extra tables, the complex data structure make the code hard to understand, we should add more comments for future's maintenance.

[bungle]

This PR has almost the same logic as the original code, but it also introduces two extra tables, the complex data structure make the code hard to understand, we should add more comments for future's maintenance.

It has less code than before and is also more performant, does less new table creations and clones, does not use pairs for looping. (On a potentially large 100.000 iteration loop).

The exact same statement can be said on your original refactor.

[bungle]

This PR has almost the same logic as the original code, but it also introduces two extra tables, the complex data structure make the code hard to understand, we should add more comments for future's maintenance.

@chronolaw comments were added. I also added another commit to clear the transformation functions.

[chronolaw]

Great job, thank you Aapo.

[team-gateway-bot]

Successfully created cherry-pick PR for master:

• https://github.com/kong/kong-ee/pull/9116