[ty] Add into_callable method for Type (#19130)
## Summary
Was just playing around with this, there's definitely more to do with
this function, but it seems like maybe a better option than having so
many arms in has_relation_to for (_, Callable).
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Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: Carl Meyer <carl@astral.sh>
