Refactor {enable,disable}-hook-handler commands.

[aadcg]

Description

These commands were suggested for deletion on #3297 but, on a closer look, I think they're in line with our goals.

I've revised the facilities.

I don't think it deserves a changelog entry.

Checklist:

• Git branch state is mergable.
• Changelog is up to date (via a separate commit).
• New dependencies are accounted for.
• Documentation is up to date.
• Compilation and tests ((asdf:test-system :nyxt/gi-gtk))
  • No new compilation warnings.
  • Tests are sufficient.

[jmercouris]

I'm not sure this is an improvement. Yes you are /technically/ removing code, but is there any real benefit? Also, do these /need/ to be commands? When would we ever use these?

[aadcg]

We'll discuss it later today.

[jmercouris]

OK!

[aadcg]

We agreed that these commands are helpful to add/remove hook handlers at run time.

The goal of refactoring the commands isn't to remove code but to improve maintainability.