For some metric expressions, column lineage isn't detected which seems to allow creating invalid metrics

A metric that looks something like...

```sql
AVG(IF(foo IS NOT NULL AND bar IN ('abc', '123') AND baz IN ('y', 'Y'), foo, NULL)) AS value
```

...will succeed and get created even if column `bar` does not exist in the upstream node. Also if all of those columns _do_ exist and this is a valid metric, `bar` doesn't show up in the column level lineage graph, even though `foo` and `baz` both do.