[Bug] Improve soft selection in completion

[dibarbet]

In the following gif, the item should either not be present (because App is considered filter text), or should be in soft selection (no exact match).

However

1. In VSCode, we do not get callbacks for filtering. So if the item is originally hard selected, we cannot change to soft selection once the list is filtered down that much.
2. In VS, it looks like we consider 'App' as part of the completion item, but not in VSCode. Potentially we need to up[date what we consider as part of the filter text.