Refile Targets Custom Function Support

[Kevin Foley]

I'd like to use an `org-ql' query in order to get eligible targets when
calling `org-refile'.

It doesn't seem `org-refile-targets' supports something like passing a
function that returns the desired targets.  Is it possible through some
other means?

If not, would a patch to `org-refile-get-targets' controlled by a new
type in `org-refile-targets' be welcome?  

Thanks,
Kevin Foley