When looking for matches for holes, prefer local bindings over top-level/in-scope module binding

[dhess]

We suspect that in most cases, when inserting a value into a hole, the student will want to use a local binding whose type matches the hole, in favor of any top-level or in-scope module binding that also matches; so we should probably implement this in the partial sort of offered bindings (aka "variables").

(Note that it may be the case that we already do this, but I'm creating this issue as a reminder to check, at the very least.)