Consider moving test modules out of system module, unless they relate to system.module

Pushed up a proof of concept, needs review for the idea.

+1 for the idea

I was literally just thinking about how to better organize all of the hook related test modules.

Since the substantive change is to the discovery I think I'll change the component.

Added complete steps to move all the identified modules if we decide to proceed with this.

Would it be possible to create subdirectories inside core/tests/modules? At least for components with many test modules (e.g., hooks).

Yes this should detect subdirectories