Custom templating: custom templates not associated with non-asset dependencies

Problem statement

When defining new custom templates declared in the config file, I couldn't introduce dependencies with other custom templates.

However, all these files all well loaded in the templates repo.

But at rendering time, all such custom files are just loaded from files and not given a namespace of dependencies like we do for asset templates.

This was annoying when trying to maintain bloated templates and trying a bit of refactoring there...

Patched the problem at home. Will share the solution with a PR if feature agreed upon.