[ty] Improve completion ranking based on origin of symbols
Part of this was already done, but it was half-assed. We now look at the
search path that a symbol came from and centralize a symbol's origin
classification.
The preference ordering here is maybe not the right one, but we can
iterate as users give us feedback. Note also that the preference
ordering based on the origin is pretty low in the relevance sorting.
This means that other more specific criteria will and can override this.
This results in some nice improvements to our evaluation tasks.
