Document that 'Track referencing basefields' must be checked to track some sources

Thank you for this! I didn't know why custom menu links weren't being tracked, and this issue helped me solve the problem.

I can confirm that enabling "Custom menu link" in source and target is not enough for menu links to be tracked in usage. You have to also enable "Track referencing basefields" in the entity usage settings. I agree that it's confusing that "Custom menu link" is enabled by default in both source and target, but it doesn't work without "Track referencing basefields," which is not enabled by default. It would make sense for either both to be enabled or both disabled. I think resolving the at-odds settings first makes sense. Documentation would certainly help, but it doesn't fix the disconnect with the default settings.

This ticket is 5 years old, so it may be outdated, but I do find that redirects work without enabling "Track referencing basefields." Some work was done on that recently, so maybe that cleared up the issue with redirects.

It seems to me from this merged commit that redirects should always have base fields tracked, but that doesn't appear to be the case based on testing I just did. It also doesn't seem intuitive to have one setting discreetly enabling a setting that you manually have not enabled.

Thanks for raising this up, it had felt outside of my radar.
In recent work we have added support for redirect and as part of that we realized it didn't make much sense to expose redirects to be used as source but not track redirect basefields, since that's the only way redirects can be linked to other entities. Because of that now if redirects are selected as source/target, we disregard the option to track basefields and also track redirects since that's the intended most specific behavior.

I would be happy to move forward the same special-casing for menu links, since that's apparently the same scenario?