Refactor scheme architecture

[aadcg]

Description

A pre-requisite to #2989, in the sense that it refactors the architecture of custom schemes in a renderer-agnostic fashion. It is a follow-up to #3341.

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 have been looking at this, and haven't found any problem yet. I will continue to review it.

[jmercouris]

Since this is often used as a predicate, perhaps consider a -p suffix.

[jmercouris]

Or at least a variant of this command that is -p suffixed that returns t/nil.

[jmercouris]

The manual command works, but not when clicked from the button on the home page.

It even works if I set the url to nyxt:manual from the home page.

home page == nyxt:new

[jmercouris]

If I click on a symbol within a code block, it also does not work. I am brought again to the debugger.

[aadcg]

The manual command works, but not when clicked from the button on the home page.

If I click on a symbol within a code block, it also does not work. I am brought again to the debugger.

I've seen these bugs before, I'll fix those.

[aadcg]

@jmercouris should be fixed, please test it.

[jmercouris]

Will do!

[jmercouris]

No problems found :-)